GitHub Milestone

You can use milestones to track progress on groups of issues or pull requests in a repository.

Milestones are kind of labels that mark and group work that are expected to be delivered at some point in time. The Milestones page, which you can access from the Issues page, clarifies that you can see the percentage of tickets completed for a particular milestone and the due date. You can also sort milestones by the due date and prioritize works within a particular milestone.

The stress here is on delivery dates and tracking progress.