autoerotism vs sex activity

autoerotism and sex activity both are nouns.

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

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

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

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