What does "fan girl" mean on social media?

A Fan Girl is someone (usually a young woman, though it can apply to anyone) who is extremely enthusiastic or passionate about a particular celebrity, band, TV show, or pop culture icon. 

For instance, if someone can’t get enough of a music artist, attends all their concerts, buys all their merch, and talks about them all the time on social media, you might hear them called a “fan girl.” Generally, the term is seen as positive, though it can hint at someone being overly enthusiastic.

“Fan girl” can also be used as a verb. When someone says they’re “fan girling” over something, it means they’re getting really excited or enthusiastic about it.