Vertical position or vertical location is a position along a vertical direction (the plumb line direction) above or below a given vertical datum (a reference level surface, such as mean sea level). Vertical distance or vertical separation is the distance between two vertical positions. Many vertical coordinates exist for expressing vertical position: depth, height, altitude, elevation, etc. Points lying on an equigeopotential surface are said to be on the same vertical level, as in a water level. A function with domain along the vertical line is called a vertical distribution or vertical profile.

The International Organization for Standardization (ISO), more specifically ISO 19111, offers the following two definitions:

ISO 6709 (2008 version) makes the following additional definition:

The International Civil Aviation Organization (ICAO) offers similar definitions:

ICAO further defines:

I.e., elevation would be the altitude of an earth-bound feature, such as the ground or a building.

Several physical quantities may be defined based on the definitions above:

Vertical distance quantities, such as orthometric height, may be expressed in various units: metres, feet, etc.