Upwind means in the direction from which the wind is blowing, or toward the source of the wind. If you stand upwind of a campfire, you're positioned so the wind blows from you toward the fire, meaning the smoke drifts away from you rather than toward you.

Sailors use this word constantly. When a boat moves upwind, it's traveling toward where the wind comes from, which requires skillful zigzag maneuvering called tacking. This is much harder than sailing downwind, when the wind pushes you along from behind.

The concept matters anywhere wind carries something you want to avoid or approach. Hunters position themselves downwind of deer so their scent blows away from the animals rather than toward them. If someone downwind of you is grilling hamburgers, you'll smell them.

The opposite is downwind, meaning in the direction the wind is traveling toward. Standing downwind of anything smelly means the wind carries that smell straight to you.