Plain English Meaning
A sit-down talk after the flight where the instructor and student go over how it went, what was done well, what needs work, and what to focus on next time.
Full Definition
A structured discussion conducted by an instructor with a student or group after a flight or training exercise to review what occurred, evaluate performance against the lesson objectives, identify errors and their causes, reinforce correct procedures, and set goals for the next session.
Context Anchor
You encounter this term in flight training, usually after landing and shutdown, when the instructor reviews the lesson with the student.
Derivation
Post-' is Latin for 'after,' and '' comes from 'brief,' meaning a short, focused summary. So a postflight briefing is literally a focused summary session held after the flight.