Software patterns document general solutions to recurring problems in all software-related spheres, from the technology itself, to the organizations that develop and distribute it, to the people who use it. Books in the series distill experience from one or more of these areas into a form that software professionals can apply immediately.
Relevance means each book presents patterns that solve real problems.
Patterns have impact when they change how people work for the better. A book becomes a part of the series not because it embraces these tenets but because it has demonstrated it fulfills them for its audience.