That gives you an extra chance to spin the reels with the Wild Symbol remaining in place for that second chance spin. Often if an additional sticky wild is struck.
This features a set of Sticky Wild symbols, and as soon as one or more of them spin in, on any reel position, they initially help form winning combinations, but will.
Expanding wilds grow to fill up an entire reel, making every spot from top to bottom wild. Sticky wild symbols "stick" in place over multiple spins, thus increasing.