IDL is a generic term for a language that lets a program or object written in one language communicate with another program written in an unknown language. In distributed object technology, it's important that new objects be able to be sent to any platform environment and discover how to run in that environment. An Object Request Broker (ORB) is an example of a program that would use an interface definition language to "broker" communication between one object program and another one.

An interface definition language works by requiring that a program's interfaces be described in a stub or slight extension of the program that is compiled into it. The stubs in each program are used by a broker program to allow them to communicate.