Milestone (noun)

1. A significant event or stage in the development or progress of something.
2. A stone marker set up on a roadside to indicate the distance in miles to a particular place.

Origin:

Early 18th century: from mile-stone, originally a stone set up to mark a mile on a road.

Examples:

1. The company's launch of a new product was a milestone in their growth.
2. The project reached a major milestone with the completion of phase 1.
3. The baby's first steps were a milestone in her development.
4. The agreement was a significant milestone in the peace process.
5. The milestone markers on the old highway indicated the distance to the next town.