In
aeronautics, the
relative wind is the direction of movement of the atmosphere relative to an
aircraft or an
airfoil. It is opposite to the direction of movement of the aircraft or airfoil relative to the atmosphere. Close to any point on the surface of an aircraft or airfoil, the air is moving parallel to the surface; but at a great distance from the aircraft or airfoil the movement of the air can be represented by a single
vector. This vector is the relative wind or the
free stream velocity vector.