Plain English Meaning

Flying in a way where the airplane is sliding sideways through the air a little, instead of moving cleanly in the direction the nose is pointed. The little ball in the turn indicator is off to one side, which tells the pilot the controls aren't balanced.

Full Definition

A flight condition in which the airplane's longitudinal axis is not aligned with the relative wind, causing the aircraft to slip or skid through the air. The inclinometer ball is displaced from center, indicating that the rudder and aileron inputs are not properly balanced for the rate of turn or the bank angle being held.