What is a Project Management Plan?
The project management plan is the master playbook: how the project will be executed, monitored, and closed. It bundles the subsidiary plans (scope, schedule, cost, quality, risk, communications, and more) plus the three baselines — scope, schedule, and cost — into one approved, living document.
The key word is approved. Once baselined, it only changes through formal change control. And it is not the schedule — the schedule is one component. On the exam, "update the project management plan" is usually the step people forget after an approved change.
Worked example
On a bridge construction project, the plan says: scope verified against drawings rev C, schedule managed in Primavera with weekly updates, changes over $50K go to the change control board, safety inspections weekly. When a design change is approved, the PM updates the cost baseline and the relevant plans — not just the Gantt chart.