inclination

Inclination is a measure of the tilt or slant of a object or feature relative to a reference orientation. It is represented as an angle, usually in degrees, and the reference plane or direction depends on the field of application. In geometry and engineering, the inclination of a line or surface describes how far it deviates from a reference plane, typically the horizontal plane. In three-dimensional geometry, the angle between a line and a plane is defined as the complement of the angle between the line and the plane's normal.

In astronomy, orbital inclination (often denoted i) is the angle between an object's orbital plane and a reference plane, usually the ecliptic or the celestial equator. Orbital inclinations range from 0 to 180 degrees; a value of 0 degrees means the orbit lies in the reference plane, whereas higher values indicate greater tilt relative to that plane.

In geology and Earth sciences, inclination (often used interchangeably with dip) describes the tilt of a rock layer, fault, or other planar feature relative to the horizontal. The dip angle is the magnitude of this tilt, measured downward from horizontal in the dip direction. This measurement helps characterize the geometry of geological structures and is essential for mapping and modeling subsurface conditions.

In everyday language, inclination also means a tendency or preference toward a certain behavior, attitude, or activity, as in “an inclination to travel” or “an inclination toward risk.” Etymologically, the term comes from Latin inclinatio, meaning a slant or bend.