The horizontal motion of the air past a given point. Winds begin with differences in air pressures. Pressure that's higher at one place than another sets up a force pushing from the high toward the low pressure. The greater the difference in pressures, the stronger the force.
The rate at which wind velocity changes from point to point in a given direction. May be speed shear, where speed changes between the two points, but not direction; directional shear, where direction changes between the two points, but not speed; or a combination of the two.