Plain English Meaning
A full once-a-year check-up of the aircraft, signed off by a specially authorized mechanic. If it has expired, the aircraft cannot legally fly.
Full Definition
A complete inspection of an aircraft and its engine required by Federal Aviation Regulations every twelve calendar months. It must be performed by a certificated airframe and powerplant (A&P) mechanic who holds an Inspection Authorization (IA), or by an appropriately rated repair station or the aircraft manufacturer. Without a current annual inspection, the aircraft is not legally airworthy and may not be flown except under a special ferry permit.
Context Anchor
Seen in aircraft maintenance records, pre-purchase checks, rental aircraft paperwork, and questions about whether an aircraft is legal to fly.