The ability of D&D and Pathfinder Druids to turn themselves into a variety of animals: a shapeshifting effect to allow Druids to become more in tune with nature, allow them to do things they normally could not or to become more fearsome in battle.
Wild Shape is one of the iconic abilities of the Druid Dungeons & Dragons and Pathfinder. It allows a Druid to take the shape of any natural animal the Druid is familiar with: birds, mammals, reptiles, fish and more. The Druid gains the physical characteristics inherent to these animals: they can fly, breathe underwater, climb better, use claws or teeth and more. They retain their mental characteristics, while gaining all physical characteristics of the animal in question: they become unable to talk, cannot manipulate objects that require hands instead of paws, and are not stronger than what is natural for these animals.
The Druid can use the ability several times per day if they are skilled enough. When they Wild Shape their gear melds with them, so they do not need to undress prior to turning into an animal (the reverse is also true). The downside to this is that unless the magic items they carried are dedicated to improving Wild Shape, they do not gain any of their bonuses.
There exist magic items, Prestige Classes, Feats and more ways to improve a Druid's Wild Shape: either by giving more uses per day, making the animals more potent, allowing creatures of unusual size or of other types than simple beasts.