A milestone is a project task with a duration of zero (0). Use milestones to mark key dates in your project, such as key decision points, approvals, and holidays. Milestones are treated like any other project task and you can create dependencies between tasks and milestones.

1. Create a project task and give the Duration field a value of 0.
2. Open the planning console Gantt chart and verify that it appears as a diamond.
   You can also convert a task to milestone through planning console.

Result