Plain English Meaning

Flying faster or slower than the situation calls for. The 'right' speed changes with what the airplane is doing and what's happening around it, so a speed that is safe in one moment can be unsafe in another.

Full Definition

A speed at which the airplane is being flown that does not match what the current situation requires — either too fast or too slow for the airplane's configuration, weight, altitude, maneuver, or environmental conditions such as turbulence or icing. Operating at such a speed places the airplane at increased risk of an upset, including stalls, loss of control, or structural exceedance.