milestone
noun [ C ]
uk/ˈmaɪlstəʊn/ us (also milepost)
an important event in the development or history of something or in someone's life:
The opening of a branch in New York represented an important milestone for the company.
a milestone in sth They described the discovery as 'a milestone in medical research'.
a time when a piece of work must be finished or something must be achieved:
In Monday mornings, we would set milestones for the week.
If they don't meet the first milestone, you withdraw support.