autoerotism vs sexual activity

autoerotism and sexual activity both are nouns.

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

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

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

autoerotism (noun)	sexual activity (noun)
using your own body as a sexual object	activities associated with sexual intercourse