What is a pattern language?

Again, from Wikipedia: "Just as words must have grammatical and semantic relationships to each other in order to make a spoken language useful, design patterns must be related to each other in order to form a pattern language. Implicit in Alexander's work is the idea that the patterns should be organized into a logical or naturally intuitive structure. The actual structure (hierarchical, iterative, etc.) may vary, depending on the topic. Each pattern should indicate its relationship to other patterns and to the language as a whole."

From The Pedagogical Patterns Project: "A pattern LANGUAGE is a set of patterns that work together to generate complex outcomes, not just solve individual problems. The patterns in the language are applied in a sequence to arrive at some complex behavior or artifact or .... Pattern Languages are GeneRative."