The Ultimate Slot Machine Glossary: 75+ Terms Every Buyer Should Know

When you start shopping for a slot machine, you run into a wall of jargon. Sellers throw around terms like EPROM, TITO, PAR sheet, and Class II like everyone knows what they mean. Most people do not, and there is no shame in that. These are industry terms from a world that was never designed for consumers.

We have been selling and servicing slot machines in Kingman, Arizona since 1992. In those 33 years, we have explained these terms thousands of times over the phone, in emails, and on our shop floor. This glossary is every one of those explanations collected in one place.

Bookmark this page. You will come back to it.

A

Accumulator Bonus — A bonus feature that builds over time as the player plays. A meter fills or objects collect on screen, eventually triggering a bonus round. Common in newer video slots from Aristocrat and Konami.

Action Button — A secondary button on some machines that triggers a feature within a bonus round, such as picking an item or stopping a spinning wheel. Not to be confused with the spin button.

Ainsworth — Australian slot machine manufacturer, part of the Novomatic group. Known for titles like Mustang Money and Eagle Bucks. We carry their machines and they hold up well.

Aristocrat — Major Australian manufacturer responsible for games like Buffalo, 5 Dragons, and Queen of the Nile. Their Viridian and MARK VI cabinets are popular with home buyers. Build quality is excellent.

Aruze — Japanese manufacturer (now called Universal Entertainment outside Japan). Known for innovative bonus features and the distinctive Innovator cabinet.

Audit Menu — A software screen accessible in service mode that shows the machine's financial and play history: total coins in, coins out, games played, jackpots hit, and more. Used by casino operators to track performance. On a home machine, it is mostly a curiosity, but it can help diagnose issues.

B

Bally — One of the oldest names in slot machines, now part of Light & Wonder (formerly Scientific Games). Famous for the Quick Hit series, Blazing 7s, and the iconic electromechanical machines of the 1960s-80s. Their Alpha and Pro Series cabinets are popular with home buyers.

Belly Glass — The glass panel on the lower front of the machine, below the reel window. It usually displays the game's logo, pay table information, or denomination. Belly glass is decorative and interchangeable. Collectors prize rare belly glass panels.

Bet Max — A button that automatically wagers the maximum number of credits per spin. On a home machine in free play mode, this is the button guests should use to get the full experience with all paylines active.

Bill Validator (Bill Acceptor) — The device that accepts paper currency and converts it to credits. Common brands are JCM and MEI/CPI. On home machines, these can be set to accept bills or disabled entirely. They are one of the most common components to need service.

Bonus Round — A special game-within-a-game triggered by specific symbol combinations. Can be free spins, pick-a-prize screens, wheel spins, or elaborate animated sequences. Bonus rounds are what make modern video slots exciting for parties. See our casino night guide for tips on machines with the best bonus rounds.

C

Cabinet — The physical enclosure that houses all the machine's components. Common cabinet types include slant-top (angled screen, player sits) and upright (vertical screen, player stands or uses a stool). Upright cabinets are more popular for home use because they take up less floor space.

Candle — The light on top of the machine that flashes different colors to signal events: service needed (steady), jackpot (flashing), or specific error codes. Originally used by casino floor attendants. On home machines, it adds to the atmosphere.

Cash Out (Collect) — The button that converts credits back to coins, tokens, or a TITO ticket. On mechanical hopper machines, pressing this triggers the satisfying cascade of coins.

Class II — A legal classification under the Indian Gaming Regulatory Act. Class II machines are technically bingo-based: the outcome is determined by a central bingo game, and the slot reels are just a visual representation. Found primarily in tribal casinos. Important for buyers because Class II machines cannot operate independently. They need a bingo server. Do not buy a Class II machine for home use unless you confirm it can be converted or run standalone.

Class III — The standard slot machine classification. Class III machines use a local RNG to determine outcomes independently. These are the machines found in Las Vegas and Atlantic City, and they are what you want for home use. Every machine in our inventory is Class III.

Coin Comparitor — The device inside the coin acceptor that verifies coins or tokens by checking their metallic composition, weight, and dimensions. Rejects slugs and foreign coins.

CRT — Cathode ray tube. The older, bulky monitor technology used in slot machines from the 1990s through mid-2000s. Heavier than LCD screens and generates more heat, but still found in many popular machines like the IGT Game King. CRTs can be replaced with LCD conversion kits when they eventually fail.

Credits — The unit of play displayed on the machine. One credit equals the machine's denomination. A $0.25 machine with 100 credits has $25.00 in play value.

D

Denomination — The value of each credit or coin the machine accepts. Common denominations are $0.01 (penny), $0.05 (nickel), $0.25 (quarter), $0.50 (half dollar), and $1.00. Most home buyers prefer quarter or dollar machines. Multi-denomination machines let you switch between them. Check our pricing guide for how denomination affects machine value.

Door Open Error — An error code triggered when the machine's main door, cash door, or top box is not fully closed and latched. The most common error on home machines, usually fixed by simply closing the door firmly until the switch clicks.

E

EPROM — Erasable Programmable Read-Only Memory. A chip that stores the machine's game software and payout percentage. In older machines (pre-2005), changing the game or payout percentage required physically swapping the EPROM chip. Newer machines use flash memory or CompactFlash cards instead. EPROMs are sensitive to static electricity. Always ground yourself before handling one.

Error Code — A numeric or alphanumeric code displayed on the machine's screen or VFD when a problem is detected. Common codes include hopper empty, coin jam, door open, and communication errors. Our error codes guide covers every code you are likely to see and how to clear it.

F

Free Play Mode — A setting that allows the machine to be played without inserting money. The machine automatically adds credits. Available on most machines through the operator menu. Essential for home use and parties. Read our complete free play guide for setup instructions.

Free Spins — A bonus feature that awards a set number of spins at no additional cost to the player. Often triggered by scatter symbols. Free spins frequently include multipliers or additional wild symbols.

G

Game King — IGT's multi-game video platform. A single Game King cabinet can hold 50-80 different games (slots, poker, blackjack, keno). Extremely popular for home use because of the variety. See our IGT S2000 guide for comparison with reel machines.

H

Handle — The lever on the side of the machine that spins the reels. Most modern machines use a spin button, but many still include a handle for nostalgia. On mechanical reel machines like the IGT S2000, the handle activates a physical switch that initiates the spin through the same electronics as the button.

Hit Frequency — The percentage of spins that result in any win, including pushes (winning back your bet). A machine with a 30% hit frequency pays something on roughly one in three spins. Higher hit frequency does not mean higher payback. It means more frequent, usually smaller, wins.

Hold Percentage — The percentage of money the machine keeps over time. The inverse of payout percentage. A machine set to 95% payout has a 5% hold. This is how casinos make money. On a home machine, the hold percentage is irrelevant since you are playing with your own money on both sides.

Hopper — The mechanical device inside the machine that stores and dispenses coins or tokens. When a player cashes out or hits a paying combination, the hopper motor spins and feeds coins through a chute into the tray. Hoppers jam occasionally and need cleaning. Our maintenance guide covers hopper care.

I

IGT — International Game Technology, the largest slot machine manufacturer in the world (now part of IGT/Aristocrat after a complex corporate history). Responsible for iconic games and cabinets including the S2000, Game King, Wheel of Fortune, and Double Diamond. The majority of home slot machines in the US are IGT products.

J

Jackpot — The highest-paying combination on the machine. On home machines, a jackpot is exciting but pays from the machine's own hopper (or adds credits in free play). Progressive jackpots, which grow with each play, require linking multiple machines or a jackpot controller.

Jackpot Reset — A procedure to clear the jackpot display and reset it to the base amount after a jackpot is hit. Done through the operator menu or a RAM clear on most machines.

JCM — A major manufacturer of bill validators. If your machine has a bill acceptor, there is a good chance it is a JCM model (iVizion, UBA, WBA). JCM units are reliable and parts are readily available.

K

Key Set — Slot machines use multiple keys for different access levels. A typical machine has keys for the main door (full access), the cash door (hopper and cash box only), the top box, and the CPU compartment. When you buy from us, you receive a complete key set. Keep spares in a safe place.

Konami — Japanese manufacturer known for titles like China Shores, Genie's Riches, and Lotus Land. Their Podium and SeleXion cabinets are well-built and popular with collectors.

L

LCD — Liquid Crystal Display. The flat-screen monitor technology used in modern slot machines. Lighter and more energy-efficient than CRT monitors. Most machines manufactured after 2008 use LCDs.

Line (Payline) — A pattern across the reels that determines winning combinations. Classic three-reel machines have 1-5 paylines. Modern video slots can have 20, 40, 50, or even 243 "ways to win" (which replace traditional paylines).

M

Max Bet — See Bet Max.

Mechanical Reels — Physical spinning reels with printed symbols, driven by stepper motors. Found in classic machines like the IGT S2000. The tactile, audible experience of mechanical reels is why many home buyers prefer them over video slots.

Metering — The machine's internal accounting system, accessible through the audit menu. Tracks total coin-in, coin-out, games played, and more. Cannot be reset without a RAM clear on most machines.

Multi-Denomination — A machine that can accept and play at multiple denomination levels (e.g., $0.01, $0.05, $0.25, $1.00). The player selects their preferred denomination on screen. Common on video slots.

Multi-Game — A machine that offers multiple different games in one cabinet. The IGT Game King is the most common example, but Bally, Aristocrat, and WMS also make multi-game platforms.

N

Nudge — A feature in some machines that moves a reel up or down by one position after a spin, potentially turning a near-miss into a win. More common in international (especially UK/Australian) machines than in American slots.

O

Operator Menu (Operator Settings) — The configuration menu accessible by authorized personnel (or the machine owner). Controls payout percentage, denomination, volume, free play settings, and more. Accessed by opening the machine and pressing a service or setup button. The exact method varies by manufacturer.

P

PAR Sheet — Probability Accounting Report. The internal document that details every possible combination on a slot machine, its probability, and its payout. PAR sheets are proprietary and rarely shared publicly. They are the mathematical blueprint of the game. If someone offers to sell you a PAR sheet, it is probably fake.

Payout Percentage (Return to Player / RTP) — The theoretical percentage of all money wagered that the machine returns to players over its lifetime. A 95% payout machine returns $95 for every $100 wagered over millions of spins. This is a long-term average, not a guarantee for any individual session. Home machines can typically be set between 85% and 98% via the EPROM or operator settings.

Payline — See Line.

Pay Table — The chart showing all winning combinations and their payouts. Displayed on the machine's glass or accessible through a help/info button on video machines. Always check the pay table to understand what the machine pays.

Progressive Jackpot — A jackpot that increases with each play, either on a single machine (standalone progressive) or across a group of linked machines (wide-area progressive). Home machines can run standalone progressives. Linking requires a progressive controller, which we can provide.

R

RAM (Random Access Memory) — Volatile memory that stores the machine's current state: credits, game in progress, error logs, and metering data. Powered by a battery when the machine is unplugged. If the battery dies, the RAM data is lost.

RAM Clear — A procedure that erases the machine's volatile memory and resets it to factory defaults. Clears all metering, error histories, and credits. Required when installing a new EPROM or resolving certain persistent errors. On most IGT machines, it involves setting a specific switch or jumper and powering on. Our error codes guide explains when and how to perform a RAM clear.

Reel Strip — The band of symbols printed on a physical reel or mapped to a virtual reel. Each reel strip has a specific number of stops (positions), and the arrangement of symbols on the strip determines the game's odds. On mechanical machines, the reel strips are literal printed ribbons wrapped around the reel cylinder.

Refurbished — A used machine that has been professionally restored to full working condition. At Used Slot Shop, our refurbishment process includes cleaning all components, testing every function, replacing worn parts, and installing new batteries. Every refurbished machine in our inventory comes with a 1-year warranty.

RNG (Random Number Generator) — The computer algorithm inside every modern slot machine that produces random outcomes. The RNG runs continuously, generating thousands of numbers per second. The number generated at the exact instant you press spin determines the outcome. There is no pattern, no cycle, and no way to predict results.

S

Scatter Symbol — A symbol that pays or triggers a feature regardless of its position on the reels (it does not need to land on a specific payline). Typically triggers free spins or bonus rounds when three or more appear.

Service Mode — A diagnostic and configuration mode accessed by opening the machine's door and pressing a service button or key. Allows access to the operator menu, audit menu, error logs, and test functions. Different from normal gameplay.

Slant-Top — A cabinet style where the screen is angled at roughly 30-40 degrees from horizontal. The player sits at a built-in shelf, similar to a desk. Popular in video poker and newer video slots. Takes up more floor space than an upright cabinet.

Stepper Motor — The precision electric motor that drives each mechanical reel. Stepper motors move in exact increments (steps), allowing the machine's computer to position each reel on a precise symbol. When a stepper motor fails, the reel may not stop accurately or may not spin at all. Replacement motors are available and the swap is straightforward.

Stop — A position on a reel where it can land. A typical three-reel mechanical machine has 22 stops per reel. Virtual reels in video slots can have hundreds of stops, which is how they achieve complex odds.

T

TITO (Ticket-In, Ticket-Out) — A cashless system that prints a barcoded ticket instead of dispensing coins. Players insert tickets to add credits or cash out to a ticket. TITO eliminated the need for coin hoppers in most casino machines after 2000. On home machines, TITO printers can be enabled or disabled. Most home buyers prefer the coin hopper experience, but TITO is cleaner and quieter.

Top Box (Topper) — The upper section of an upright slot machine, above the main screen. May contain a secondary display, a bonus wheel (like Wheel of Fortune), an LCD topper for animations, or simply a backlit glass panel with the game logo. Top boxes are often removed for home use to reduce the machine's overall height.

Top Glass — The backlit glass panel at the top of the machine displaying the game name and graphics. On many machines, this is removable for transport. See our moving guide for tips on removing top glass safely.

Touchscreen — An LCD screen with a touch-sensitive overlay, allowing players to interact by touching the screen. Common on video slots and multi-game machines. Touchscreens can be recalibrated through the service mode if they become inaccurate.

Tournament Mode — A special configuration that tracks play for competitive purposes. Some machines have built-in tournament modes that display rankings, time remaining, and scores. More commonly, tournament scoring is done manually with a scoreboard.

U

Upright — A cabinet style where the screen is vertical and the player stands or sits on a separate stool. The most common cabinet type for home use because it takes up the least floor space (roughly 20" x 20" footprint).

V

VFD (Vacuum Fluorescent Display) — The small text display panel, usually green or blue, found on the front of many slot machines. Displays credit count, bet amount, win amount, and error messages. Brighter than LED text and visible in any lighting condition.

Video Poker — A poker game played on a slot machine, most commonly five-card draw. The player is dealt five cards, chooses which to hold, and draws replacements. Payouts are based on the resulting poker hand. Available as standalone machines or within multi-game platforms like the Game King.

Video Reels — Virtual reels displayed on a video screen rather than physical spinning reels. Allows for more complex games with more reels, more stops, and animated features. Most machines manufactured after 2003 use video reels.

Volatility (Variance) — A measure of the risk profile of a slot game. High volatility games pay less frequently but with larger wins. Low volatility games pay more frequently with smaller wins. For home use and parties, low-to-medium volatility games are more fun because players win more often.

W

Ways to Win — An alternative to traditional paylines. Instead of specific line patterns, a machine pays for matching symbols on adjacent reels regardless of their vertical position. A 5-reel machine with 3 rows has 243 ways to win (3 x 3 x 3 x 3 x 3). Popularized by Aristocrat's Buffalo and adopted widely.

Wild Symbol — A symbol that substitutes for other symbols to complete winning combinations, similar to a wild card in card games. Some wilds have multipliers (2x Wild doubles the win) or are sticky (remain in place for multiple spins).

WMS (Williams/WMS Gaming) — Manufacturer known for innovative bonus rounds and licensed themes. Created the Bluebird and Bluebird 2 cabinets and games like Monopoly, Zeus, and Wizard of Oz. Now part of Light & Wonder. WMS machines have some of the most entertaining bonus features for home use.

Numbers and Symbols

243 Ways — See Ways to Win.

3-Reel vs. 5-Reel — Three-reel machines are the classic style: simpler, faster, and nostalgic. Five-reel machines offer more paylines, more features, and more complex gameplay. Most home buyers start with a three-reel machine and add a five-reel later. Our buyer's guide helps you decide which is right for you.

5-Reel — A machine with five spinning reels (mechanical or video). Allows for more paylines and more complex bonus features than three-reel games. The IGT S2000 five-reel and Bally five-reel uprights are popular choices.

Quick Reference: Terms You Will See When Shopping

When browsing our shop or any used slot machine listing, here are the terms you will encounter most often:

• Cabinet type: Upright or slant-top
• Denomination: What coin value the machine plays (quarter, dollar, etc.)
• Class III: Standard standalone operation (what you want for home use)
• Multi-game or single-game: How many games are in the machine
• CRT or LCD: The screen type
• TITO or coin: How the machine handles payouts
• Refurbished: Professionally restored with tested components

If you see a term in a listing that is not in this glossary, call us. We have been answering these questions since 1992, and our free lifetime tech support means you are never on your own.

Still have questions? Contact us or check out our complete buying guide to start shopping with confidence.