This is a two-day planning event where all of the people working in an agile release train (ART) get together to plan the work for the next programme increment (PI). The duration of the PI is typically 8-12 weeks and is agreed in advance and applies to all teams in the ART.
The teams forecast the features that they will be able to deliver during the PI and work with other teams to identify, understand and resolve dependencies between teams, and risks to feature delivery. Objectives are agreed for each team and for the PI so that it is clear what each time is expecting to achieve by the end of the PI and also what the ART expects to achieve as a team of teams.