A term with several meanings.

Data can mean a collection of facts, numbers or information; the individual values of which are often the results of an experiment or observations.

If the data are in the form of a table with the columns consisting of variables and the rows consisting of values of each variable for different individuals or values of each variable at different times, then data has the same meaning as data set.

Data can also mean the values of one or more variables from a data set.

Data can also mean a variable or some variables from a data set.

Properly, data is the plural of datum, where a datum is any result. In everyday usage the term ‘data’ is often used in the singular.

See: data set

Curriculum achievement objectives references
Statistical investigation: All levels
Statistical literacy: Levels 2, (3), (4), 5, (6), (7), (8)