What is Wild symbol?
A wild symbol is a slot symbol that substitutes for other symbols to help complete winning combinations, usually excluding scatters and bonus symbols.
When a wild lands on a payline next to matching symbols, it counts as whichever symbol produces the best win. For example, two cherries followed by a wild on the third reel can pay as three cherries.
Studios have built many variants on the idea. Expanding wilds grow to cover a whole reel, sticky wilds stay in place for several spins, walking wilds move one position each spin, and multiplier wilds apply a multiplier to any win they help form. Wilds typically do not replace scatter or bonus symbols.
Wilds are part of a game's maths model, so a game with frequent or powerful wilds does not necessarily return more. Their effect is already included in the stated RTP. How often wilds appear is set by the reel layout, not by recent results.