Plain English Meaning
Flying the airplane straight ahead without turning, keeping the wings level and the nose pointed in the same direction.
Full Definition
Flight in which the airplane maintains a constant heading along a straight ground or air path, with the wings held level and no intentional turn being made.
Context Anchor
Used early in flight training when learning basic airplane control, especially while holding a steady direction by outside visual reference and cockpit indications.
Derivation
“Straight” comes from an older meaning of “stretched ” or “, not bent.” That helps here because straight flight means the airplane’s path is not curving into a turn.