The Project Management Plan is a document that defines how the project is executed and controlled

The Project Management Plan includes:

• Scope Management
  
• Schedule Management
  
• Cost Management
  
• Quality Management
  
• Resources Management
• Procurement Management
  
• Risk Management
  
• Communications Management

The Project Management Plan is subject to approval by the Project Sponsor.

You can download a template here

See the wikipedia Project Management Plan article