A feeling of deep admiration and adoration a girl has for another girl. The girl with the girl crush usually doesn't want to date the other girl, but wants to be exactly like them in every way and wants to be their best friend. The girl with the crush usually loses their identity in the process of trying to be like the crush-ee.
Hannah: I think I have a girl crush!
Susan: Really? On who?
Hannah: On that Sarah girl. She's super pretty, funny, and nice! I want to be just like her!