Fangirl is
one who obsesses over celebrities, fictional characters, et cetera. These delicate creatures can also be known as ‘Otakus’, but typically an
otaku is
one who spends all day inside, alone, and watching
anime. You could very easily say that a very large proportion of tumblr users are, in fact, fangirls.
However, fangirl isn’t just a name; it’s also and action. For example, you could say you ‘fangirled’ over something, meaning you had a moment in which you probably squealed
like a pterodactyl over something/someone.
Fangirls are VERY sensitive about their OTP’s, so be careful what you say in front of them...