1. A fan of something (female) who is obsessed with the said subject to a certain degree (normally unhealthy).

2. A general term for a female fan of something.

A fangirl is a (female) fan of a character from a movie, anime, video game, etc. or a real life actor or singer. Usually they have an obsession with their "idol" and do various activities to show their love for the said idol. Such activities include ranting about them, making shrines or fanlistings, creating graphics (wallpapers, layouts, etc) that feature the "idol", writing fanfics and making fanart. Some also make plushies or collect posters and other merchandise of their beloved idol.

Usually, members of this label are seen as 1) insane; 2) idiotic; or 3) scary.

However, not all fangirls are like this. Quite a few of them are just an average fan of something, and just call themselves such. But, there are three types of commonly seen fangirls:

1) BELOW AVERAGE FANGIRL

This fangirl is the least likely to cause chaos or mayhem, insult or annoy someone else who is not a fangirl (or boy, if they happen to be male). They admit that they have a slight obsession for something/one, and are mature about it. While they might use smilies (XD, XP, ^_^) and occasionally rant, they try not to go overboard about it.

2. AVERAGE FANGIRL

This fangirl is the most commonly seen fangirl across the Internet, and are generally harmless. They are prone to making shrines, annoying people with their "fantasies" of ...

Current occupying invaders of Quizilla, these monstrous creatures spam relentlessly, squandering bandwidth and making the site run slower than your granny on downers. Their weapon of choice is the crappy fanfic, typically written about a character or actor whom they only like because he's hot, even though he usually isn't.

A bunch of hell-crazy girls who will glomp, tackle or try to almost kill their idol.
Can also be considered really evil.

A stereotypical denomination given to a female who even SLIGHTLY likes an actor or movie character. Usually assigned by a bigot who wants to make themselves look good by making others look ditzy.

A girl with an obsession of something. Can be a celebrity, anime, a band e.t.c. popular obsessions are Orlando Bloom, Elijah Wood, Inuyashamashywhaever, and Good Charlotte. Most of them do have lives outside of their crush apart from the odd scary one. They can produce quite good fanart and fanfiction. Many are good-looking and thin (e.g. many of my friends). Many are also nice people who are capable of answering a question with 'squee' or 'OHMYSEXGAWD'. I am a fangirl and proud.

A term that can apply to a wide variety of things.

1. The Stereotype
Stereotyped fangirls are, as the name suggests, a caricature of a fangirl's main traits; these being a complete and total obsession with their fandom. They tend to rant on forums, draw really bad fanart and drool over online fanfiction describe messy slash rapage. And Mpreg. *shudders*

2. By Far More Realistic Fangirl.
These fangirls are not quite as disturbingly devoted to their obsessions. Sure, they will write and read fanfiction and discuss characters on forums, but they understand the utter futility of declaring that Riku, or Cloud Strife, Orlando Bloom or who the hell is their fandom is THEIRS for eternity, and they will disembowel you with their katana if you touch their pixelated lovers.
Normal fangirls also don't stalk. Because stalking is bad and an easy way to get arrested.

A female fan of an actor and/or fictional character. Usually between the ages of 12-14. Is known to utter high-pitched sounds whenever the object of their obsession's name is mentioned. Claims that, "IM reelly gona marry him cuz we R ment 2 b!!!!!!!11111!!!!!!@#$347903458134!@!@!" Uses excessive amounts of punctuation. This condition is usually just a phase and doesn't generally last extremely long. However, in the more severe cases the fangirl can go on in her fangirlyness for years on end.