What is the irregular and instantaneous motion of air called?

The irregular and instantaneous motion of air is called turbulence. It is a form of fluid motion marked by chaotic, rapidly changing pressure and velocity rather than smooth, parallel layers.

Turbence develops when a flow has enough kinetic energy to overcome the stabilizing effects of viscosity. Swirling eddies of many sizes form and interact, increasing mixing, friction, and the transfer of heat and momentum. The contrasting flow pattern is laminar flow, in which fluid moves in orderly layers.

The word applies well beyond aircraft. Turbulence appears in fast rivers, smoke rising from a chimney, surf, storm clouds, and air moving around buildings or mountains. In aviation, passengers usually notice it as bumps or sudden changes in altitude, but the aircraft is passing through moving air rather than encountering literal holes or pockets.

A related term is clear-air turbulence, which occurs without visible clouds, often near jet streams where air masses move at different speeds. Wake turbulence is another specialized type, produced by vortices behind an aircraft’s wings. Physicists study turbulence statistically because its irregular behavior is extremely difficult to predict in detail.