Meaning
A significant point or achievement marking key progress in a project timeline.
Three examples from work
Project review
PMWe reached a major milestone today: the alpha version is officially in internal testing.
ExecutiveCongratulations team; that keeps us on schedule for the public launch.
Contract delivery
ClientWhen will we review Milestone Two deliverables?
Account LeadThe milestone review meeting is scheduled for next Tuesday.
Risk planning
LeadThe third-party API integration delay is putting our Q3 milestone at risk.
PMLet's escalate to their partnership manager immediately.
Phrases include 'hit a milestone', 'reach a milestone', and 'milestone deliverable'. Milestones represent outcomes, not just calendar dates.