copulation vs sexual activity

copulation and sexual activity both are nouns.

Word	Noun	Adjective	Verb	Adverb
copulation	Yes	No	No	No
sexual activity	Yes	No	No	No

As nouns, sexual activity is a hypernym of copulation; that is, sexual activity is a word with a broader meaning than copulation:

copulation: sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur
sexual activity: activities associated with sexual intercourse

Other hypernyms of copulation include sex, sex activity, sexual practice.

copulation (noun)	sexual activity (noun)
sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur	activities associated with sexual intercourse