watershed

(UK, Australia) The topographical boundary dividing two adjacent catchment basins, such as a ridge or a crest.

(figurative) A critical point marking a change in course or development.

(US, Canada) A region of land within which water flows down into a specified body, such as a river, lake, sea, or ocean; a drainage basin.

(UK, Canada) The time of day after which material of a more adult nature (e.g., violence, swear words, or nudity) may be broadcast on television or radio, either one permitted by law or one contrived from convention (e.g. when children are not watching).

Serving to mark a significant development, change in direction, etc.