Complex websites and web applications can be created by combining configurations of Modules, Fields, Content Types, Menus, Blocks, Categories, Roles / Permissions, etc... This site setup and configuration process is a very time consuming and repetitive bottleneck.
The Patterns module is built to bypass this bottleneck by managing and automating site configuration. Site configuration is stored in YAML, XML, or PHP files called Patterns. These files have a structure which is easy to read, modify, manage, & share and can be executed manually or as a part of an automated web site deployment.
A fairly complete and up to date documentation is available here: