Veja
http://stackoverflow.com/questions/3678665/is-there-still-a-difference-between-a-library-and-an-api
A library is a collection of functions / objects that serves one particular purpose. you could use a library in a variety of projects.
A framework is a collection of patterns and libraries to help with building an application.
An API is an interface for other programs to interact with your program without having direct access.
To put it another way, think of a library as an add-on / piece of an application , a framework as the skeleton of the application, and an API as an outward-facing part of said app.
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