It provides a different or translated view of that class. It effectively offers an impedence-matching facility. The Adapter pattern allows otherwise incompatible classes to work together by converting the interface of one class into an interface expected by the clients. Socket wrenches provide an example of the Adapter. A socket attaches to a ratchet, provided that the size of the drive is the same.
Bridge is designed up-front to let the abstraction and the implementation vary independently.
Adapter is retrofitted to make unrelated classes work together. Adapter provides a different interface to its subject. Proxy provides the same interface. Decorator provides an enhanced interface. Adapter is meant to change the interface of an existing object.