What is the definition of a project charter?

1. A short document that grants the project manager the right to continue working on the more detailed planning phase of a project
2. The project purpose or justification statement, that answers the question "why" and helps all parties understand the purpose of the project
3. A high-level description of what needs to be accomplished and how it will be done
4. A document that represents the knowledge acquired and captured by the team throughout project planning and execution