"A pattern is a careful description of a perennial solution to a recurring problem within a building context, describing one of the configurations which brings life to a building. (Please note that we don't require that the submitted patterns represent "perennial solutions.")"
"Each pattern describes a problem which occurs over and over again in our environment, and then describes the core solution to that problem, in such a way that you can use the solution a million times over, without ever doing it the same way twice."
"A pattern language is a network of patterns that call upon one another. Patterns help us remember insights and knowledge about design and can be used in combination to create solutions."
References: Public Sphere Project