As we’ve seen, online slots free the computer-controlled guts from a modern slot machine’s physical limitations. Or, a little less dramatically put, they allow software designers of online games to come up with new and creative ideas on the skeleton of the basic ‘reels and paylines’ slot design.

The fundamental features of an online slot are ‘scatters’ and ‘wilds’.

• Scatters are symbols that can pay no matter where they end up on the screen (i.e., it doesn’t need to be on a payline to get the reward). Scatters are often used as triggers for a bonus round or a ‘special’ reward, and generally bear either a logo or a main image related to the theme of the slot.

• Wilds are exactly like wild cards in a card game. They’ll complete a winning combination by acting like the needed symbol on the payline. However, they can’t act as a scatter symbol…but they can (and often do) provide an extra bonus if you get three or more wilds. And some games even have special wilds, like ‘expanding wild’ games in which a wild symbol can cover all of the spaces in its row, enabling more and bigger winning combinations.

The ‘advanced’ features of online slots include some fairly innovative ideas, from unusual payline arrangements to additional bonus rounds.

Many online slots have a ‘free spins round’ where you are awarded a number of (guess what?) free spins. Usually there will also be some kind of multiplier in effect for the duration of the spins, and sometimes this is also where the expanding wilds show up. The best kind of free spins is a ‘re-triggerable’ free spins round, which means that you can get another free spins round from the current round, and so on…

But the very best kind of bonus round (in my opinion) is the ‘second screen bonus round’, where you play a different game to win additional rewards. The simplest form of these is the gambling game, where you can guess the next card’s color or other attribute to multiply your win (many don’t even consider this a second screen bonus round, because it’s typically available every time you win anything during a normal spin).

More involved second screen bonuses include ‘pick a box’ games, where you have a number of items arranged on the screen and a certain number of tries to get the good stuff hidden underneath. You can find quite a few of these at any given online casino, USA or elsewhere.

The most impressive second screen games are actual animated games, like arcade games, in which your skills play a part in racking up the bonuses. The games based on Marvel comics and Tomb Raider are excellent examples of how this can be used to bridge the gap between online slots and full-on video games.