Wild symbols in slot machines are a wildcard that substitutes for regular symbols to help complete or extend the value of a winning combination. You also see the wild symbol referred to as a wild card simply because its job is to act as any other regular symbol on the reels.

For those of you new to video slot machine gaming, regular symbols link up to give you a combination win; therefore, the wild does not substitute for scatter or bonus symbols that trigger in-game features.

Wild symbols can also come with modifiers applied to them:

Multiplier: Each time a wild lands inside a symbol combination to help complete it or extend it, a multiplier can be applied to the value of that combination win.
Expanding Wilds: Expands vertically to cover all positions on the reel
Walking Wilds: With each spin, the wild will remain on the reels and move left or right until it drops off.
Sticky Wilds: The wild will remain on the reels for a set number of spins. It can stick to the reels after a non-winning spin, for a re-spin, and more commonly during free spins bonus games, where the wild will typically remain until the feature ends.
Jumping Wilds: Jumping wilds are similar to Walking Wilds, except they can move up, down, and skip a reel after every spin. They constantly change positions randomly.
Stacked Wilds: This feature is when a wild spins on the reels in vertical clusters. They can stack 2, 3 or 4 symbols high or more, depending on the slot game.

Wilds can appear both in the base game and during bonus rounds, significantly enhancing the potential for big payouts. Additionally, you may find that software providers develop different modifiers to the ones mentioned above.

Key takeaway: Wild symbols substitute for regular symbols to help improve your chances of landing combination wins, while they also commonly come with a variety of modifiers.