A project plan, according to the Project Management Body of Knowledge (PMBOK), is: “…a formal, approved document used to guide both project execution and project control. The primary uses of the project plan are to document planning assumptions and decisions, facilitate communication among project stakeholders, and document approved scope, cost, and schedule baselines. A project plan may be summarized or detailed.
The latest edition of the PMBOK (v5) uses the term project charter to refer to the contract that the project sponsor and project manager use to agree on the initial vision of the project (scope, baseline, resources, objectives, etc.) at a high level. In the PMI methodology described in the PMBOK v5, the project charter and the project management plan are the two most important documents for describing a project during the initiation and planning phases.