meter reading vs datum

meter reading and datum both are nouns.

Word	Noun	Adjective	Verb	Adverb
meter reading	Yes	No	No	No
datum	Yes	No	No	No

As nouns, datum is a hypernym of meter reading; that is, datum is a word with a broader meaning than meter reading:

meter reading: a datum about some physical state that is presented to a user by a meter or similar instrument
datum: an item of factual information derived from measurement or research

Other hypernyms of meter reading include data point.

meter reading (noun)	datum (noun)
the act of measuring with meters or similar instruments	an item of factual information derived from measurement or research
a datum about some physical state that is presented to a user by a meter or similar instrument