What is a milestone in project management?

A milestone is a significant point or event in a project schedule that marks the completion of a major deliverable, phase, or decision point. Milestones have zero duration because they represent a moment in time, not a span of work. Examples include project charter approval, design review completion, user acceptance testing sign-off, and go-live date. Milestone charts provide a high-level summary view of the project schedule for executives and stakeholders who do not need activity-level detail.