A fangirl is a female with a very constant dedication/obsession with a fictitious character, actor, singer, band, etc...
The act of fangirling can involve hand waving, fluttering eye-lids, lip-biting, squeals, continuous "OMG"s being sung, many Instagram/Tumblr/Facebook/Twitter posts surrounding whatever was fangirled over, etc....
Fangirl 1(average): OMGOMGOMG!!! Did you hear One Direction's new single that came out its so amazayn!!!! I stayed up all night to listen to it!! I totally love them and their songs. The music video is awesome! Harry looks totally hot. Do you guys agree? :)

Fangirl 2(overboard ass-face): Back down b****, Harry is mine, We are getting married. You aren't even a real fan!

or
Fangirl 2(overboard ass-face): OMG! Harry looks totally hot in this picture! <3

Fangirl 1(average):IKR!

F 2: BACK OFF!

Hater: Hes an uggly ass face! UGGH!

F1: @hater thats mean :(

Hater: @F1 watevs you stupidass

F1: *assembles troops of directioners

F1 and Directioners: WE HATE YOUUUU!

:)
by 1derfully-disney February 9, 2013
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A bunch of freaks that obsess over a singer /actor / fictional character.
Fangirl #1: "OMG DID YOU SEE THAT PICTURE OF (*insert celebrities name here*)"

Fangirl#2: "OMG ASJKSAKDSKLKSAD HE IS LIKE SO HOT OMG WERE GETTING MARRIED."

Friend of celebrity: Freaks..
by MrTobiasSmith April 6, 2012
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A young female, generally between the ages of 12 and 19, that is obsessed witha pacticular fictional character and the actor who plays him/her. Avoid fangirls at all costs especially in large groups as they tend to swarm and if you are unlucky enough to catch them near their object of admiration, cover your ears and run. They have a batlike shriek that can be heard for miles. Also known as stalker in training
by sherlockedgirl January 22, 2014
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a person whom is dedicated to a certain idol. This person has no life, and is okay with it. They usually spend their time on Twitter, Tumblr, Instagram, and/or facebook fangirling about their idol. They are also a part of a fandom. It is extremely addicting and needs a warning label.
"I am a professional fangirl."

"What are you doing when you get home?"

"Oh, just going to fangirl."
by soccerchic365 November 12, 2012
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FANGIRL. : a Person who is an extremely or overly enthusiastic fan of someone or something.
FANGIRL: Everyone became a fangirl when Emma Watson walked in the room
by Princess pink February 21, 2015
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A girl who will do anything to see her obsession. Fangirls mainly of boy bands,anime,actors, and or fictional characters. Usually have more knowledge on them then they're own family. WILL CRY THERE EYES OUT AT THE CHANCE TO MEET THE OBSESSION. These girls belong to fandoms. never insult a girl on her fandom or else. (This is a warning.)
Fangirl: HARRY IS SO HAWT I WANNA MARRY HIM AND KISS HIS FACE!!!
by Fangirl 2.0 January 3, 2015
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*sees magazine stand*
"DIIIIDDDDD SOMEONESEEEE SSAYYYYYYY JOSHIFERRRRRRRRRRRRR???!!!!!!!!"

Person 1: was that a Fangirl I heard?
Person 2: yeah, I think it might have come from Australia
by Why hello there, fandom June 27, 2014
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