turbulence

Short definition from Wiktionary

Noun

1. 1
   The state or fact of being turbulent or agitated; tempestuousness, disturbance.
2. 2
   Disturbance in a gas or fluid, characterized by evidence of internal motion or unrest.
3. 3
   Specifically, a state of agitation or disturbance in the air which is disruptive to an aircraft.
4. 4
   An instance or type of such state or disturbance.