What is a milestone? It a way to tell how far your project has progressed. Take a look!
What is a milestone? A project milestone, that is. Simple: a project milestone is just a marker in time when you evaluate your project. Normally, you evaluate to make sure your on track. Is everything finished that should be finished for that milestone? Can we proceed to the next milestone at this time. Everything is squared away and ready to move on?
Milestones are just zero-duration tasks
When you set up a new milestone, you are really just adding a new project task. That task has a duration of "0" to differentiate it from normal tasks. When you do that, you see a diamond symbol in the Gantt chart to signify the marker in time where the milestone occurs.
Milestones in olden times
Originally, milestones were stone obelisks set up next to the road. When you walked from one town to the next, you passed these stones which told you how many miles you had walked. So if the next town was ten miles away, you counted ten milestones and then you knew the town was just around the corner.
The same is true in projects. Milestones mark how far you have come in a project. And they help tell how far you must go to complete it. They are just like the stone obelisks of old, except that you can easily move them.
You can track time to milestones!
Normally, you do not track time to milestones. They are intended as markers or reminders of progress. But you can log time to them just like any other project task. They can be configured to show up in the timesheet like tasks, which means you can log time to them and compare that time to your original estimates. If you don't want them to show up in the timesheet, unselect the 'Quick Task' checkbox.