Difference between API and IDL

Question

Both API and IDL act as an interface between two components of software and play the role of bridge between two components of software or between two software.

What is the difference between them?

Answer 1

API is a concept. It is any external programming interface that a piece of software exposes so that it can accept external input from some other software, run some logic, and provide output. Usually when we talk about API's, like Facebook's Graph API, or the Windows API, we are talking about the types and logic contained within those API's, and how they can be used.

IDL, as the tag says, is a language you can use to describe a API, in a manner that other software may understand. It is platform independent, so can be used to facilitate integration. More information about this language is vastly available if you search for it ;)