Datum /(?)/

Da·tum

Datum

n.

pl. Data

  1. Something given or admitted; a fact or principle granted; that upon which an inference or an argument is based; -- used chiefly in the plural.
    Any writer, therefore, who . . . furnishes us with data sufficient to determine the time in which he wrote.
    — Priestley.
  2. a single piece of information; a fact; especially a piece of information obtained by observation or experiment; -- used mostly in the plural.
  3. The quantities or relations which are assumed to be given in any problem. (Math.)
  4. a point, line, or level surface used as a reference in measuring elevations. (Surveying)

Phrases & Compounds
Datum line
the horizontal or base line, from which the heights of points are reckoned or measured, as in the plan of a railway, etc.