Define:
A facade is an object that provides a simplified interface to a larger body of code, such as a class library.

Traits:
make a software library easier to use, understand and test, since the facade has convenient methods for common tasks
make the library more readable, for the same reason
reduce dependencies of outside code on the inner workings of a library
wrap a poorly designed api with a better one

Usage:
When you want to expose a simpler interface to a complex underlying implementation