Online Slots Terminology – A Beginner’s Guide

A Beginner’s Guide to Online Slots Terminology

  1. Reels
  2. Paylines
  3. Coin size
  4. Paytable
  5. Bonus Round
  6. Free Spins
  7. Click and Pick
  8. Minigame
  9. Multiplier
  10. Multiplier Meter
  11. Wilds
  12. Stacking
  13. Expanding
  14. Sticky
  15. Scatters
  16. Tumbling Reels
  17. Gamble Feature
  18. Progressive Jackpot
  19. Return to Player
  20. Volatility



The reels have the symbols on them and spin vertically.  Classic fruit machines generally have 3 reels but most modern slots, on and offline, have 5.  A 5 x 3 arrangement, with 5 reels and 3 symbols visible when the reels stop, is the most common but there are many variations.


Classic fruit machines only had one payline running across the middle of the reels, where the winning combinations needed to appear in order to trigger a payout.  Online slots usually have multiple paylines (although some have the option of choosing to play fewer lines) and some, such as the Microgaming 243 way slots and the IGT MultiWay Xtra slots, do not have paylines in the traditional sense at all, but are based on left-to-right combinations of symbols regardless of where they appear on the reels, and on symbols that appear next to each other.

Coin size

This is the basic bet.  On slots with traditional paylines it is equivalent to the bet per line, but on multiway slots it will be a specified amount shown on the screen.  Sumatran Storm, for instance, has 720 ways to win and the bet per spin fixed at 60 coins – so with a coin size of 1p you’d be betting 60p per spin and with a coin size of £1 you’d be betting £60 per spin.


The paytable is where you’ll be able to see which combinations of symbols pay out, and how much they pay out.  Here’s where coin size is important as the payouts are specified in coins to accommodate any size stake and any number of lines played.  Here’s an example.



Bonus Round

This is a special part of the game that certain winning combos will take you to.  Some slots have several different bonus rounds.  A bonus round can consist of free spins (either carried out on the same reels or on a different set of reels with higher paying symbols), a click and pick or a minigame (or combination thereof).  Everyone likes to trigger the bonus round as they (a) are fun to play and (b) have big potential payouts.

Free Spins

This is the most common type of bonus round.  A certain combo (typically three or more scatter symbols) triggers it and awards a number of free spins that will be specified in the paytable.  These will play out automatically.  During the free spins bonus round, there will be additional elements increasing the size or frequency of wins.  This could include any combination of the following: different reels with higher paying symbols, extra wilds, stacked wilds, expanding wilds, extra scatter, extra paylines, a score multiplier, a way to trigger even more free spins.

Click and Pick

In this type of bonus round, you will be presented with two or more  items on screen to choose between and click on and these result in various awards, either directly when they are mystery box type items or indirectly (such as in Racing For Pinks where you choose between two cars and are awarded a multiplier if the car you choose wins the subsequent race).  The awards can be payouts, multipliers, free spins or in the case where the click and pick is combined with a free spins round they could be extras for the free spins such as extra wilds.


This type of bonus round is rare and perhaps the best example is the starship defender game in Star Trek Against All Odds.  This is a skill based section where the points you score affect your maximum score in the rest of the bonus round.  In the Star Trek game, there are three levels of bonus wheel to spin and your score in the skill section determines which level you get (although you can skip the minigame and be given a random selection).


A multiplier multiplies your payout – e.g a 3x multiplier gives you three times as much.  This could be for the current spin, the next spin or as is common with bonus rounds, a set number of spins or the duration of the bonus round.

Multiplier Meter

A multiplier meter has a series of multipliers that are triggered by consecutive wins.  Each winning spin causes the meter to move one space and applies the new multiplier to any winnings from the following spin.  When the run of wins comes to an end the meter typically reverts to x1.  Big Bang is an excellent example of this feature and it is also often found in combination with a tumbling reels type feature as in Gonzo’s Quest.


A wild symbol is one that can substitute for another symbol in a payline – so Q,Q, Wild would score the same as Q,Q,Q.   Typically a wild can substitute for all symbols apart from the jackpot and the scatter that triggers the bonus round – details will be in the paytable.  Sometimes bonus rounds can contain features that designate additional symbols as wild.  In some slots, the wild is a multiplier; in that case, supposing it was a 2x multiplier, the Q,Q, Wild combo would score twice as much as Q,Q,Q.


This is when a particular symbol appears several times on a same reel, all together to form a vertical stack.  Wilds can be stacked in the bonus round and sometimes in the base game and increase the likelihood of getting several winning combinations.  Other symbols can also be stacked; in D&D Treasures of Icewind Dale, for instance, a different symbol stacks dynamically with each spin.


An expanding wild turns adjacent symbols wild as well, either horizontally or vertically, increasing the chances of getting several winning combos.  This can happen as part of a bonus round or in the case of some slots wild reels can be randomly awarded during play.


A sticky symbol is one that remains stuck in place for a respin.  Some slots have sticky wilds (usually just in the bonus round) and some, such as the Jack Hammer games, have sticky wins.  The respins continue until there are no new wins.


Paylines and ways to win are irrelevant in the case of scatter symbols.  If three scatters pay out (or trigger the bonus round), they can appear anywhere on any of the reels.  This means that if the bonus round in the slot you are playing is triggered by scatters, the chances of getting it are the same whether you play 1 line or 100 lines (but the bonus round payouts usually depend on bet size, so you’d win 100 times as much in the case of the 100 line play).

Tumbling Reels

In this type of slot invented by IGT, when there is a payout all the symbols that form part of a winning combo disappear and new symbols tumble down from the top of the screen to fill the gaps.  It’s basically sticky wins in reverse, and can be triggered several times in a row.  Other providers now have similar game engines but they have to be called something other than tumbling reels as only IGT can use that term – Williams and Gamesys, for instance, both call it Cascading Reels.

Gamble Feature

Slots with a gamble feature allow you to gamble the proceeds of a winning spin (or sometimes the proceeds of an entire bonus round).  It is usually a simple double-or-nothing gamble on whether the machine will turn over a red card or a black card, but a few slots such as Microgaming’s  Untamed: Wolf Pack have a more sophisticated gamble feature available.

Progressive Jackpot

In a progressive jackpot slot, all the instances of the slot (or group of slots) at different sites are networked together, and each time someone places a bet a portion of that bet is added to the central jackpot.  The jackpot is started off at a certain amount and grows with every spin until someone, somewhere gets lucky and wins the lot – after which it is reset to the seed amount again.

Return to Player

This is the percentage of stakes that the slot pays back out to the players, averaged over hundreds or thousands of spins.  Note that it is a percentage of stakes and not a percentage of deposits.

Progressive jackpot slots generally have a lower return to player than both slots in general and the non-progressive version of the same slot, to allow for the contribution that has to be made to the central jackpot fund from every spin.


Volatility is a measure of how much the slot is likely to deviate from the average return to player in a play session – and how many spins are needed before the actual return to player settles down close to the expected return to player.  If that sounds like gobbledegook, consider this:  A slot with a very high paying and rather rare bonus round but not much of a payout during normal play has high volatility – do 100 spins on that and the chances are you’ll either come out ahead after triggering the bonus round at least once, or you’ll have lost most of your stake after not triggering it at all.  With a low volatility slot – which has smaller more regular payouts either during normal play or as a result of  a more frequent and less extreme bonus round, the amount you will have left after 100 spins will tend much closer to the theoretical return to player.

Many players prefer the excitement of a high volatility slot but do remember that you can lose a lot of money very quickly on one of those without ever getting to the exciting bit!