Milestone

gs:Milestone Class

A dated point of progress in a project. schema.org has no milestone type; schema:Event is the nearest base. Linked to its project with schema:about, because schema:superEvent accepts only an Event. Status and dates follow the Open Contracting Data Standard milestone.

Identifier (IRI)
https://schema.govfresh.com/v1/Milestone
Subclass of
schema:Event
Profile
projects

The full definition is in the vocabulary file (Turtle). A static host cannot choose a format by request, so this page and that file are the two ways to read it.