in the ‘starting up a project’ process, what is the PRINCE?

In the PRINCE2 methodology, the 'project mandate' is the term used for initial documentation that triggers the start of a project, typically provided by corporate or program management. It can often come in the form of a request for proposal received by an external supplier, setting out the initial definition of the project and what it aims to achieve, which then leads to more detailed project definitions in the 'starting up a project' process.References: PRINCE2® 7 Foundation resources on project initiation documentation.