The concept of the project management plan is one of the most fundamentally important things that the project management team and the project management team leader needs to know in order to properly and most effectively manage a project from start to finish. Specifically speaking, the project management plan refers to a particular and unique input and output divide that consists of a formal and approved document or set of documents that ultimately and completely defines how exactly the project is executed, managed, monitored, and controlled. The plan in some cases may be very carefully and completely detailed, or in some others, it may be more broad stroke, presented in more of a summary style format. It may be composed of one and many more subsidiary management plans, and may also be composed of any number of other planning documents. It is important that the project management plan be determined at an early stage of the project management process.
This term is defined in the 3rd and the 4th edition of the PMBOK.