'Each pattern is a three-part rule, which expresses a relation between a certain context, a problem, and a solution.

As an element in the world, each pattern is a relationship between a certain context, a certain system of forces which occurs repeatedly in that context, and a certain spatial configuration which allows these forces to resolve themselves.

As an element of language, a pattern is an instruction, which shows how this spatial configuration can be used, over and over again, to resolve the given system of forces, wherever the context makes it relevant.' (christopher alexander, well i don't have his book so used this quote out of a comment of richard gabriel)

'A pattern is the abstraction from a concrete form which keeps recurring in specific non-arbitrary contexts.' (Dirk Riehle, Heinz Züllighoven)

'A pattern is a named nugget of instructive information that captures the essential structure and insight of a successful family of proven solutions to a recurring problem that arises within a certain context and system of forces ... a pattern does more than just identify a solution, it also explains why the solution is needed!' (Brad Appleton)