Wind is the movement of air. Moving air is a fluid, behaving in many ways like water. However, air is 1000 times less dense than water and is limited to moving much smaller materials.

People often refer to wind as if it has a constant speed and direction (e.g. a west wind at 30 mph), but most wind flow is not that uniform. The usual condition is turbulence, with eddies and pockets of air moving up or down or sideways or backwards at different speeds. The reported wind speed and direction are statistical averages of the wind conditions. Wind direction is always reported as the direction the wind is coming from (a west wind is moving from west to east).

Friction between the moving air and a surface slows down the wind. Thus, winds are generally stronger with height above the ground. In the United States and worldwide, the standard height for wind measurements is 10 m (~33 ft) above the ground. Sand movement on beaches and dunes depends on wind conditions near the surface.