Datum is, from its Latin origin, a singular form of "data", and may refer to a single item of data.
Singular data point
Geodetic datum, a standard position or level that measurements are taken from in geographic surveying
Datum reference, in carpentry, metalworking, needlework, geometric dimensioning and tolerancing
Chart datum, level of water depth on a nautical chart
Datum or datum point, a (possibly arbitrary) reference baseline or point from which scientific measurements are made (from a Latin meaning of datum as a "given", i.e. an accepted fact)
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