Yaw

(*) 1. The rotation of an aircraft, ship, or missile about its vertical axis so as to cause the longitudinal axis of the aircraft, ship, or missile to deviate from the flight line or heading in its horizontal plane. 2. Angle between the longitudinal axis of a projectile at any moment and the tangent to the trajectory in the corresponding point of flight of the projectile.
  

Angular deviation of the projectile from its line (axis) of flight.