Wild symbols were one of the first features that could be seen on slot machines since the introduction of the first 3 reel slots. These symbols give the game an extra dimension and behave in the same manner as the joker in a card game – they can represent any of the other symbols to form a winning combo from a losing one.
For instance, if you have 4 matching symbols with a wild on a 5-reel payline, the wild will stand in as the fifth identical symbol. Therefore, you’re paid as if you have five in a row.
Some general rules about wilds are they can’t replace a Scatter symbol, nor can they substitute bonus icons or free spins. While some wilds are high-paying symbols in some games, with 3 or more netting you a considerable win, in other games, they have no value of their own.
An expanding wild as the name suggests work by expanding to fill the whole reel up or down, making all symbols on the reel wild. This has the potential of generating multiple wins over many paylines.
The expanding wild symbol appears randomly on a reel, and it is impossible to control when, where, or how it lands. Some real money online slot games only have them on specific reels. For example, some 5-reel games allow them only on reels two, three, and four.