The name for the land area that separates two watersheds is a watershed divide or drainage divide.

Here's a breakdown:

* Watershed: An area of land where all the water drains to a common point, like a river, lake, or ocean.

* Divide: A line or area that separates different watersheds. It can be a ridge, mountain range, or even a subtle change in elevation.

So, the watershed divide is the boundary that dictates where water flows – one side of the divide will drain into one watershed, and the other side will drain into another.