expansion vs annotation

expansion and annotation both are nouns.

Word	Noun	Adjective	Verb	Adverb
expansion	Yes	No	No	No
annotation	Yes	No	No	No

As nouns, annotation is a hyponym of expansion; that is, annotation is a word with a more specific, narrower meaning than expansion:

Other hyponyms of expansion include amplification, elaboration, annotating, subjoining, subjunction, supplementation.

expansion (noun)	annotation (noun)
the act of increasing (something) in size or volume or quantity or scope	the act of adding notes
adding information or detail	a comment or instruction (usually added)
a discussion that provides additional information
a function expressed as a sum or product of terms