Plain English Meaning

Taking off while looking at the cockpit instruments instead of out the window, because you can't see well enough outside to fly by sight.

Full Definition

A takeoff performed by reference to flight instruments rather than outside visual cues, used when visibility is restricted by low clouds, fog, darkness, or precipitation. The pilot uses the attitude indicator, heading indicator, airspeed indicator, and altimeter to maintain runway alignment, control , and a stable from onward.