datum

Datum is a singular noun for a single fact or data point. It derives from the Latin datum, meaning “something given.” In modern English, data is usually treated as a plural noun or as a mass noun, while datum survives in technical contexts to denote one element of information or a starting premise.

In statistics and data science, data denotes a collection of measurements or observations used for analysis. A datum is one member of that collection, such as a single temperature reading. Although data is commonly treated as plural, in many fields it is used as a mass noun.

In geodesy and surveying, a datum is a reference frame or surface used to define coordinates. A geodetic datum ties coordinates to a mathematical model of the Earth, such as an ellipsoid, and can be global or local. Examples include WGS 84 and NAD 83, which underpin coordinate systems for maps and GPS.

In philosophy, a datum can mean a thing given to the mind by experience, serving as a basis for reasoning. In computing and information processing, a datum is a basic unit of information or a data item stored in a field, as distinct from larger structures like records or datasets.