An Etymological Dictionary of Astronomy and Astrophysics

1. General: The angle between one plane and another, or the angle formed by a reference axis and a given line.
   

2. Binary systems: The angle between the plane of the orbit and the → plane of the sky.
   

3. Rotating stars: The angle between the → equatorial plane and the → plane of the sky.

See also: → angle; → inclination.