Plain English Meaning
The aircraft is pointing downward — the nose is below the horizon line you see ahead of you or on the attitude indicator.
Full Definition
A flight attitude in which the aircraft's nose is pointed below the horizon relative to the natural horizon or attitude indicator reference line. It is one of the basic unusual attitudes recognized and recovered from during instrument and primary flight training.
Context Anchor
You will see this term when learning aircraft control, correcting student errors, practicing recovery from unusual positions, and describing what the airplane is doing by looking outside or at the .