Plain English Meaning
The aircraft ends up doing something the pilot did not intend, and the pilot cannot get it back to flying or moving the way it should. It is the official label used when an accident happens because the airplane stopped responding to control inputs the way the pilot needed it to.
Full Definition
An accident category in which the pilot is unable to maintain or regain control of the aircraft within its intended flight parameters, resulting in an unintended departure from controlled flight. It includes events such as stalls, spins, and unrecoverable upsets, and is categorized as occurring either in flight (LOC-I) or on the ground (LOC-G).
Context Anchor
Seen in accident , discussions, and instructor training when describing how an accident developed.