As revealed in the lyrics to the song by Megan Thee Stallion, it's a spree of fucking other women's boyfriends (while calling those women hoes), but only if they spend a lot of money on the self righteous hoe. When these hoes are questioned about the meaning of "hot girl summer" they respond with vague euphemisms about being free and unapologetically yourself (aka shameless hoes), ignoring the lyrics of the song, the behavior they themselves apply it to, and ironically not confident that this behavior is justifiable when described honestly.
"Lil' thundercat, throw it back, he can't handle that
I'on want to talk unless a nigga finna throw a stack
Bad attitude, but I'm cute so he call me bae
I'ma need that head, give me neck like a vertebra
Check my body, oochie wally, where ya' wallet?
If I take yo' nigga it's nothing you can do about it (not at all)"