1. Horizontal direction or bearing. Compare azimuth angle.
2. In navigation, the horizontal direction of a celestial point from a terrestrial point, expressed as the angular distance from a reference direction, usually measured from 0° at the reference direction clockwise through 360°.
An azimuth is often designated as true, magnetic, compass, grid, or relative as the reference direction is true, magnetic, compass, grid north, or heading, respectively. Unless otherwise specified, the term is generally understood to apply to true azimuth, which may be further defined as the arc of the horizon, or the angle at the zenith, between the north part of the celestial meridian or principal vertical circle and a vertical circle, measured from 0° at the north part of the principal vertical circle clockwise through 360°.
3. In astronomy, the direction of a celestial point from a terrestrial point measured clockwise from the north or the south point of the meridian plane. See horizon system.
4. In surveying, the horizontal direction of an object measured clockwise from the south point of the meridian plane.
In surveying, an azimuth of a celestial body is called an astronomic azimuth.
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use