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The return to player (RTP) value is expressed in percentages and is the same as the inverted house edge, a term more commonly used for classic games like blackjack and roulette. A house edge of 2% means that the casino has the upper hand by a magnitude of 2%, over a statistically significant number of game rounds. In simplified real money terms this means that for every £100 put in £98 will be returned to the player and will translate to a slot RTP = 98.0% (which is exceptionally high but found in for instance NetEnt’s Blood Suckers), as long as you stick to your game plan and play flawlessly with optimal strategy.

RTP is always provided in the games’ rules, and as a rule of thumb it is advisable to stay away from slots with an RTP below 95%, unless it is a jackpot game in which the worse odds are compensated for by the enormous prizes - even as the jackpot is rarely included in the RTP measure.

With video slots, the optimal strategy and decision making elements are taken out of the picture, but remember, this is a theoretical measurement which only holds true over thousands of game rounds. In the short run a player might lose £100 or win twice as much, and the closest an individual will get to an accurate RTP is their entire lifetime gambling.

RTP is a theoretical measure only valid in the long run, typically thousands of spins.

To add to this the random number generator does not have a memory and luck is not spread evenly over every casino player, it is chaotic. Ten consecutive spins in a row without a hit does not mean the odds will increase for the eleventh spin. Assuming it will is what in academic circles is called ‘The Gamblers Fallacy’. Some players will win, and some will lose and pay for those winnings - which side one ends up on is uncertain, and only time will tell. What is for certain though is that the casino will most definitely make some money in the process as they have the odds in their favour.

For the RTP to be correct - something frequently tested by unbiased parties and gambling authorities - winning spins will need to be balanced out by losing ones, and the house edge. Over time wins minus wagers made and the house edge will settle around the RTP – how big the fluctuations above and below this baseline is what variance is all about.

Some slot games will be highly volatile, meaning that they will not pay out anything for a long time and suddenly explode and deliver an ‘EPIC MEGA WIN’. Other slots will frequently pay smaller sums and never really surprise you with those massive wins. Low variance slots will still pay out some decently sized wins every once in a while, but nothing life changing.

Variance and volatility are used interchangeably in the world of slots.

If a slot has a high or low variance is rarely stated but there is a way to at least get a hint of a slot game’s character. In general, a good indication of a certain slot’s variance can be found in the pay table:

• The spread between the highest winning combination and the lowest paying is the first thing to look at.
• Take this in combination with the maximum win available on a single round, this usually corresponds to the game’s bonus or free spins round.

Since we are big fans of NetEnt slots, let us take two examples from their impressive game portfolio.

Low Variance Slots

Let’s start with a low variance game, the well-known Starburst slot. It boasts a maximum win of 50,000 coins. The lowest paying winning combination equals 5 coins, this doesn’t even cover the minimum bet mind you, which is 10 coins. The highest paying combination is 5 bar symbols and will give you 250 coins. Also note the maximum coin win at 50 000 coins.

High Variance Slots

For the high variance example we have picked another NetEnt classic, Piggy Riches. Unfortunately we don't have a review of it, it is an old game that feels rather dated, but we mention two other highly volatile slots below which we recommend over it. We chose Piggy Riches simply since the maximum win is spelled out: 360 000 coins (we have edited in the upper part as it was a bit too dark to see at paytable screen). In the land of the luxurious pigs the lowest win is 5 coins. The highest paying win though is several times bigger and clocks in at an impressive 2000 coins.

Games without the maximum win clearly spelled out are usually low variance, but this is not always true. For instance NetEnt’s Gonzo’s Quest and Dead or Alive are both reputable for their high variance, but none of them openly state the maximum coin win available.

Approximating Variance

By taking the highest paying regular win and divide it by the smallest we can create a baseline which can be used to quickly gauge a slot's variance. For low variance games, we will be looking at a value somewhere around 50, and for high variance games, it will be somewhere in the area of 400.

It should be quite obvious given what we have learned about RTP - that wins needs to be balanced against the losses and house edge - that the two games above are very different in character. The high variance slot (Piggy Riches) can have you bleed like a pig for quite a while until you hit it big, while the low variance slot (Starburst), despite its’ name, rarely will pay any astronomical amounts but frequently burst out smaller, less stellar wins.

A great way to think about variance and its relation to RTP is that the highly volatile games will require more rounds before the wins and losses have balanced out. Conversely a low variance slot will take fewer rounds. Which one is better? This is simply a matter of taste: you risk more to win more, or vice versa.

Bonus tip: in the early stages of clearing a casino bonus, a potentially successful strategy can be to play high variance slots. If you hit it somewhat big, switch to a low variance game and grind out the rounds till you meet the wagering requirements. But beware; many casinos will consider this bonus abuse, so make sure to read the T&C and that there is no mention of this kind of behaviour being forbidden.

Over the years game mechanics in video slots has evolved at an almost exponential rate. The one armed bandits usually came with three reels, showing three rows each. Wins were created by lining up 3 of the same symbol in a horizontal or diagonal line from the leftmost wheel. Today, winning combinations are much less rigid, reel positioning and design are much more flexible, and different bonus features abound.

In spite of the almost endless possibilities, there are still recurring functions that make up the foundation of any well designed online slot, and knowing the terminology will help you understand almost any video slot. Some principle will guide how symbols are generated (reel layout), how symbols interact (in terms of special features), and then ultimately how wins are made (win mechanic).

This will not in any way be an exhaustive list of terms, but we will do our best to give you a solid base to stand on. Note that a Free Spins mode is not the same as the kind of Free Spins found among top casino bonuses.

How wins are made is the most important thing to understand and here we find three main concepts. Just as with features and how the reels are spun there will slight variations and combinations, which in turn opens up almost endless possibilities.

Win Ways

Way wins, or win ways, as the name implies has to do how many ways wins can be created. The standard reel layout in a video slot consists of 5 reels that each show 3 rows of symbols. To create a win, at least 3 identical symbols are needed, starting from the reel from the left. The exact position of the same symbol doesn’t matter as long as they land on adjacent reels, starting from the first reel from the left. With wins created by combining 3-5 symbols there are 243 different ways to win (3x3x3x3x3).

Win ways can also be employed with reels showing more symbols on each reel, and even work from both directions; creating wins from both left to right and right to left. The defining feature is that the exact symbol positions are irrelevant, as long as the reels are next to each other and identical symbols are present, a win is valid.

Yggdrasil's Dark Vortex is a feature rich Win (both) Ways slot, check it out for a great example on this game mechanic action - not for the faint of heart and a highly volatile slot!

Paylines

Paylines are simply predetermined patterns that identical symbols need to land on in order to be valid. They are usually zig-zagging from left to right over the reels, or going in straight horizontal lines. Paylines can always be found in the game rules, but are also commonly marked with numbers just outside of the board – hovering over (tapping if on mobile) the number will usually highlight the path.

We won’t give any examples here as this is by far the most frequently used win mechanic. If a game allows you to adjust the paylines, then it is always advisable to use the maximum number as it makes for much more exciting game play, but don’t forget to reduce the bet size accordingly.

Cluster Wins

Clustered, or grouped, wins is a rather new concept. With this, mechanic wins are created by groups of adjacent symbols, both vertical and horizontal. This mechanic is mainly used in games with larger than standard reel layouts, and in slots with cascading reels.

Good examples are found in NetEnt’s ‘Cluster Pays’-series (Aloha! and the Legend of Shangri-La), but the crown jewel in the category is PLAY’n GO’s Gemix.

This pertains to how reels are spun, or rather how they actually do not spin. Instead of the classic rotating wheels, in a slot with the cascading reels mechanic, symbols fall down from above and are stacked on top of each other.

Symbols, usually blocks, that are involved in a win will be removed, and the symbols above will fill the now empty space. The additional empty space on top will then get filled with another random symbol, and hopefully the rearranged board will create another win. These games usually make use of a multiplier that increases by every consecutive win.

With a cascading reel mechanic symbols fall down from above and are stacked on top of each other.

The most prominent slot game with cascading reels is NetEnt’s Gonzo’s Quest, and the game developer has actually trademarked their version of the cascading reel mechanic referring to it as an ‘Avalanche’ feature.

‘Swooping reels’ is another term used for the same concept, a name that the developer Quickspin uses. A slot that is worth checking out from them, which employs the mechanic, is Big Bad Wolf, game of the year 2013. The slot about the three little pigs, and the big bad wolf has been updated several times over the years and still feels fresh. That it boasts an RTP of 97.3% doesn’t hurt either!

To trigger bonus games or free spin rounds, a Scatter Symbol is often used. The design of it varies, and the name refers to the fact that it does not need to lay on a payline (or make a way win) to trigger its’ function. Usually 3 or more must land on the reels, but they can be scattered over the board and still produce a win, or activate a bonus feature.

Sometimes a game will employ a bonus symbol which will not be of the scatter type. Mega Fortune Dreams for instance does this, and requires the Bonus Symbol to lie on a payline in order to trigger the bonus feature.

Re-Spins and Sticky Symbols

Another rather self-explanatory term, a re-spin is simply another spin contained within the same game round. This feature is in most cases triggered in combination with a wild symbol, and in nine out of ten cases also involves sticky symbols in some way. A sticky symbol is exactly what it sounds like, a symbol that carries through to the next game round. See the section below on wilds for further info.

Wild symbols are the most frequently used among the special symbols in modern video slots. It works as a stand in for any regular symbol, and helps create the best possible win. This concept has evolved over the years and it is common to make use of Stacked Wilds, which means that the wild symbol appears in stacks of two or more on the same reel.

Expanding, Sticky and with Re-Spins

This ties into another type of way that the wild can be manipulated, by expanding. If the game has an Expanding Wild feature, a wild that lands on a reel expands vertically, usually filling up the entire reel with wilds. Turning the single wild into a stacked one.

A wild that triggers a re-spin is usually referred to as Sticky Wild Re-Spin feature; if a wild lands on a reel, it sticks to that position and triggers a re-spin, if another wild lands on the re-spin that one sticks as well and triggers an additional spin. This can go on ad infinitum, or at least till you’ve filled out every wheel with wilds. This is, for instance, how the jackpot in Yggdrasil Gaming’s Joker Millions is triggered.

Combining wilds with other features is, as we’ve been through above, a proven method to bring a lot more action to the game. The star in Starburst is a prominent example of how the wild can be utilised in several ways, and a perfect fit to demonstrate everything we’ve learned so far about wilds.

• When the star - the wild symbol in Starburst - lands on a reel, it first expands fillin the reel, then
• Wins are collected and a re-spin is triggered with the stacked wilds stuck to the reel during the next spin.
• More stars will trigger an additional expansion and a re-spin, ad infinitum.

The reason Starburst is so extremely popular is certainly because of this feature, which is very easy to understand, but incredibly effective in the sense of raising the excitement, and increasing the size of the win. Pure genius, and a perfect example of how less often means more when it comes to slots.

Walking

Another much more innovative variety of the Sticky Wild Re-Spin feature is the Walking Wild, as can be found in the Jack and the Beanstalk slot. When this lands on a reel an eventual win is first collected, then the wild symbol moves to an adjacent reel, when in place a re-spin in triggered. This repeats until the wild has walked out of the screen.

Wild Toro from ELK Studios is another good example where wilds are combined with a re-spin in an innovative way. Watch the raging bull chase the matador over the field leaving wilds behind - and the matador? We leave that for you to find out.