nonhorizontal

Nonhorizontal is an adjective used to describe objects, lines, surfaces, or orientations that are not parallel to the horizon. It covers any tilt away from the horizontal, including oblique angles and vertical orientations. The term is used across disciplines to distinguish from horizontal elements.

In two-dimensional geometry, a line is nonhorizontal if its slope is not zero; conversely, a horizontal line has zero slope. The steepness is measured by the angle θ between the line and the horizontal axis, with θ not equal to 0° or 180°. In three-dimensional contexts, a surface or line is nonhorizontal when it is not parallel to the horizontal plane; equivalently, its direction or normal vector has a vertical component.

Nonhorizontal features appear in surveying, architecture, cartography, computer graphics, and art. For example, a road that climbs a hillside is nonhorizontal, as is a vertical wall, a slanted roof, or an oblique line drawn in a plan. In typography, oblique or slanted text is sometimes described as nonhorizontal relative to standard upright type.

Related terms include horizontal, vertical, oblique, tilt, and slope. The term emphasizes orientation relative to the horizontal axis or plane and is used to describe deviations from a level or flat reference frame.