a girl or woman that you are having a romantic relationship with [↪ boyfriend]:
He's never had a girlfriend.
He lives in Chicago with his girlfriend.
split up/break up with your girlfriend (=stop having a romantic relationship)
one of my ex-girlfriends (=former girlfriends)
I didn't have a steady girlfriend (=one you have a long relationship with).
2 especially American English
a woman or girl's female friend:
She's out with one of her girlfriends.