The word ‘milestone’ is used extensively but often means different things to different people. In the project management world people happily use the term all the time, but we need to remember that a milestone will mean different things to different teams within a project. One thing we can probably agree on is that they come at the end of some activity and they have zero duration because they symbolize an achievement, a point of time in a project.
Here we use milestone for a task of zero duration that shows an important achievement in a project (it may be an event for celebration. Milestones are a way of knowing how the project is advancing if you are not familiar with the tasks being executed.
If you are involved in setting some milestones or trying to resolve a problem relating to them, our FAQ on setting project milestones may come in useful, we certainly hope so.