a point, line, or level surface used as a reference in measuring elevations.

(n) A theoretically exact point, axis, or plane used as a reference for tabular dimensioning. A datum marks the origin from which the location and orientation of geometric features are established.

The quantities or relations which are assumed to be given in any problem.

The horizontal plane to which soundings, ground elevations, or water surface elevations are referenced. Some examples of a datum are: Mean high water Mean higher high water Mean low water Mean lower low water Mean sea level Mean tide level National Geodetic Vertical Datum

Something given or admitted; a fact or principle granted; that upon which an inference or an argument is based; -- used chiefly in the plural.

a single piece of information; a fact; especially a piece of information obtained by observation or experiment; -- used mostly in the plural.

a statement accepted at a given value (face value); Latin datum is neuter past participle of dare (to give), hence 'something given'. (a "given"). NOTE : term data, the plural of datum, is used more often in English.

an empirical fact

A specific spot assigned as the basis for measurement when doing an archaeological excavation.

Imaginary line from which all measurement of arms are taken.

an item of factual information derived from measurement or research

a fixed horizontal line from which all heights and depths can be calculated and measured.