Difference between data and datum

Data, like a lot of technical and academic words, comes from Latin. It used to be considered as a collective singular noun. In formal documents — for scientific or scholarly writing — data is mostly used as the plural of datum.

Yet, for those of a non-scientific background, data is common for both singular and plural use. It’s acceptable to write a sentence as ‘translation data is available on their website.’ Data is a mass noun. Mass nouns denote something that cannot be counted. When you refer to a small piece of data, this may be called datum.

Definition

Data (mass noun, plural)

Facts on which a decision is to be based.

Facts to be processed by a computer.

Datum (singular noun)

Item of data

In addition, there are plural forms that do not end in S as listed below.

Source: OED