A project plan, is a series of structured tasks, objectives, and schedule to a complete a desired outcome, according to a project managers designs and purpose.
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.
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.
The plan should be agreed and approved by at least the project team and its key stakeholders.
Many project management processes are mentioned in PMBOK® Guide, but determining which processes need to be used based on the needs of the project which is called Tailoring is part of developing the project management plan.