Definition
The direction of the airflow with respect to the wing, produced by the airplane moving through the air. Relative wind is parallel to and opposite the flight path of the airplane.
Plain English
The wind the wing actually feels as the airplane moves through the air. It always flows toward the wing from the direction the airplane is heading, so if the airplane is moving forward, the relative wind comes straight at it from the front.
Context Anchor
Seen in stall awareness and wing-control discussions, especially when explaining how the wing meets the air before and during a stall.
Derivation
Relative' comes from the Latin 'relatus,' meaning 'carried back' or 'in relation to.' The wind is called 'relative' because it isn't the actual weather wind blowing across the ground -- it's the wind relative to the moving wing. Whether the air outside is calm or gusting, the wing still feels a wind created by its own motion through the air.
Why Pilots Care
It sets the angle at which air meets the wing and is essential for recognizing when a stall is about to occur.
Analogy
Stick your hand out a car window on a still day. The car isn't driving into a weather wind, but you still feel air rushing against your hand from the front. That rushing air is the relative wind -- created by your motion, not by the weather.
Grounding Statement
If the airplane is descending through the air, the relative wind comes from the opposite direction of that descent, so it may meet the wing from below compared with level flight.
Intuition Check
Relative wind is not the same as the weather wind reported at an airport. It is the airflow the airplane experiences because it is moving through the air.
Example Sentence 1
The angle of attack is the angle between the wing's chord line and the relative wind.
Example Sentence 2
When the pilot raises the nose, the relative wind strikes the wing from a higher angle.