Like other interface description languages, IDL defined interfaces in a language- and machine- independent way, allowing the specification of interfaces between components written in different languages, and possibly executing on different machines using remote procedure calls.
References
David Alex Lamb, Sharing intermediate representations: the interface description language, Ph.D. Dissertation, Carnegie-Mellon University, Department of Computer Science, 1983
David Alex Lamb, "IDL: sharing intermediate representations", ACM Transactions on Programming Languages and Systems9:3:297-318 (July 1987)
John Nestor, Joseph M. Newcomer, Paola Gianinni, and Donald Stone, IDL: The language and its Implementation, Prentice-Hall, 1990.
Richard Snodgrass, The Interface Description Language: Definition and Use, W.H. Freeman, 1989