Hmm, I'm curious what that phrase means exactly? I've never heard it before.
It's a term taken from the book "The Pragmatic Programmer" by Andrew Hunt and David Thomas. It is defined as: "every piece of knowledge must have a single, unambiguous, authoritative representation within a system".In Eric Raymonds book "The Art Of Unix Programming" in the chapter on Design, he goes into more detail about Compactness and Orthogonality which I think explains the concepts rather elegantly.