If something moves upwind, it moves in the opposite direction to the wind. If something is upwind, the wind is blowing away from it.

What does it mean to be upwind of something?

: in the direction from which the wind is blowing.

Is it upwind or downwind?

As adverbs the difference between downwind and upwind

is that downwind is in the same direction as the wind is blowing while upwind is in the direction from which the wind is blowing.