What is a Milestone?
A milestone is used to mark an important progress point within a project. A milestone often marks a progress point within a project that must be reached by a certain date in order to keep the project on schedule.
A project can have many milestones.
Milestones can be used to segment a project into intervals to allow early indication of issues with the project schedule.
Milestones can provide a quick view into the tasks whose completion by certain dates is critical. The Milestones tab shows all milestones in one view and whether or not they are ahead of schedule or behind schedule.