Wind is air moving relative to the Earth's surface, reported by the direction it comes from and the speed at which it travels. A north wind blows from the north toward the south, and speed is given in knots, miles per hour, or meters per second depending on the product.
What makes air move
Air flows in response to a pressure gradient force, which points from higher pressure toward lower pressure and sets air in motion. The larger the pressure difference across a given distance, the stronger the force and the faster the resulting wind.
As soon as the air is moving, two more forces act on it. The Coriolis effect deflects moving air to the right in the Northern Hemisphere, and friction with the surface slows it and turns it back toward lower pressure. Above the boundary layer, the balance of pressure gradient and Coriolis produces the geostrophic wind, which flows parallel to the isobars.
How forecasters use it
Surface winds tell a forecaster where boundaries lie, where moisture is being transported, and where convergence is squeezing air upward. Winds aloft describe the flow storms will be steered by and the shear a storm can use to organize an updraft.
The change of wind with height matters as much as any single level. Directional turning through the lowest kilometer supports low-level rotation, and speed increase through the deeper layer above supports the tilted, long-lived updrafts that organized severe storms rely on.
Important limits
A reported wind reflects the sensor's location, height, and exposure. A gauge shielded by trees or buildings reads slower than the open air a few hundred meters away, and a surface report over rough terrain says little about the flow one thousand meters up.
Winds also fluctuate on time scales the observation may not capture. A two-minute average smooths out gusts, and a peak gust says nothing about the sustained flow feeding a storm. Reading wind for storm forecasting means looking at layers and trends, not single numbers.