What does datum mean?
A datum is a single item of information — one fact, measurement, or observation — considered individually rather than as part of a larger collection. It is the singular of "data," and the two words carry a strict grammatical relationship: just as one cannot properly speak of "a data" in formal usage, careful writers use "datum" when they mean exactly one piece of evidence. The word appears most often in scientific, statistical, and scholarly contexts, where precision matters; a researcher might note that no single datum supports a conclusion without the weight of many more. Beyond information science, "datum" also has a specialized sense in surveying and engineering, where it denotes a fixed reference point — such as sea level — from which all other measurements are taken. Though increasingly rare in casual speech, it remains valuable wherever exactness about individual facts counts.
A single item of information, especially one forming the basis of a calculation or inference.
"Each temperature reading served as an independent datum in the climatologist's analysis."
Preferred over "data" in formal contexts when referring to exactly one item of information.
In surveying and engineering, a fixed reference point or level from which measurements are taken.
"All elevations on the site plan were calculated relative to the ordnance survey datum."
Common in technical fields such as geodesy, cartography, and construction.
The plural "data" is far more common than the singular "datum" in modern usage, and is frequently treated as an uncountable mass noun in everyday contexts.
"The data were collected over three years, with each datum carefully verified before inclusion."
Technically, every spreadsheet you've ever opened is full of "data" — but each single cell holds just one "datum." Most people never make the distinction.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of datum
Datum comes directly from Latin, where it meant literally "something given" — the neuter past participle of the verb dare, meaning "to give." The word entered English in the mid-seventeenth century, adopted into scholarly discourse alongside its plural "data" to denote items of accepted information from which conclusions could be drawn. It shares its Latin root with related English words such as "date," "dative," and "donate," all of which trace back to dare and the notion of giving.
Related word forms
How datum is actually used
Strictly, "datum" is singular and "data" is plural, and this distinction is still respected in formal, academic, and scientific writing. However, "data" is now very widely treated as a mass noun taking singular verbs in everyday usage, so "datum" appears mainly in technical registers where precision about a single observation matters.
Easily confused with datum
"Data" is the plural form referring to information collectively, while "datum" refers to one individual piece of that information.
A "date" is a particular day or point in time, whereas a "datum" is an item of factual information.