An onshore wind is any wind that blows from a body of water toward land. An offshore wind is any wind that blows from the land toward body of water.
Explanation:
The onshore winds are winds that form over larger bodies of water.
These winds move from the body of water toward the land, usually during the day.
The reason for that is that the bodies of water have lower temperature during the day, so the air above them is cooler, denser, so it moves toward the less dense, warmer air over the land.
The offshore winds are winds that form over land.
These winds move from the land toward a body of water, usually during the night.
The land heats up faster than the water, but also cools off quicker than the water, so at night the land is cooler. Because of it, the air masses that form over the land are more dense, so they move toward the less dense air masses over the water bodies.
