A milestone is an important event in a project. It represents a moment in time wherein the team members have achieved an important event for the project. Thus, it should be assigned zero duration. Milestones are crucial in project management as they can add value to the project scheduling. It allows project managers to determine if their projects are on schedule or not. Simply put, they are used to monitor the progress of the project.
This is the reason why project managers need to create a milestone list. It is a list that identifies all the milestones of the project. It also indicates if a particular milestone is critical which is required by the contract or optional for the project. Optional milestones are usually based on historical information from a similar project.
It is the responsibility of the project manager to create the milestone list. Since it is a project management document, it requires the necessary inputs from the project team members. Inputs for this particular project document include the scope baseline, schedule management plan, organizational process assets, and the enterprise environmental factors.
This term is defined in the 5th edition of the PMBOK.