These are Definitions for Acronyms and Terms you'll find in Fan Fiction.

H/C - hurt/comfort. The writer introduces a grievous injury to a main character so the other character(s) can nurse him/her through, all the while exploring boundaries, relationships, talking, comforting, etc. Some writers use this as an excuse to bring characters together romantically. It is a classic scenario that appears often as a plot device driving a relationship.

A/U - alternate universe. This device allows an author to either pretend certain events never took place, or to do things to chracters that would never happen in the "real" world. For instance, in a Highlander AU, Richie Ryan and Kronos can interact because Richie never died.

UST - Unresolved sexual tension. Two characters pine away and long for one another, but never consumate their feelings. Mulder and Scully's relationship was the very epitome of UST.

PWP or Lemon - 'Plot? What Plot?' or 'Porn Without Plot'. is a classification of Fanfiction pieces whose main purpose is to convey an explicitly sexual situation between at least two characters from a particular fandom, and in which plot, characterization or any other artistic mean take secondary importance, if present at all.

het - heterosexual. Denotes a story where all the romantic or sexual relationships are between opposite sex partners, as opposed to same sex (see slash, above).

angst - Heart-wrenching drama. Trauma. Worry and trouble. Internal conflict.

beta reader - Someone who proofreads your story, picks out the punctuation and grammatical errors, points out your plot holes, and tried to help you make it better. A really good beta reader, who takes time to work with you extensively and is honest and thorough, is worth his/her weight in gold.

disclaimer - A statement at the beginning of the story which informs the reader that borrowed characters/scenarios and settings were not created by the writer, but were used and manipulated. Example: "The characters of Dana Scully and Fox Mulder were created by Chris Carter and are the property of 1013 and Fox television. This story was not written for profit." It's important to clarify that you haven't made money off the story, because selling fan fiction for profit opens the writer up to a lawsuit.

feedback - Giving or receiving opinions and constructive criticism. When you ask for feedback on your story, be prepared to get both positive and negative comments, and remember, an honest opinion is sometimes better than a large amount of gushing praise (though we all like the gushing praise).

relationshipper (or 'shipper) - a fan who is in favor of a romantic relationship between two heretofore platonic characters, such as Harm and Mac, Mulder and Scully, etc.

spoilers - details which give away the plot of an episode or movie. If you use these in a story, it's best to warn the reader up front in your disclaimer, or you'll be flamed.

flames - nasty, rude or angry comments about something you have done wrong (or that someone perceives you have done wrong), written in a way that does not have any consideration for hurting your feelings. Generally, it's a personal attack. The experience of being flamed is not pleasant.

troll - a newsgroup term which refers to a person who makes it their consuming passion in life to be as consistently obnoxious, rude, disgusting and otherwise offensive as possible, by posting ignorant comments and flaming others who post. Their primary objective is to get a rise out of the reader.

gen - general themes fan fiction, which doesn't fall into a specific category above, such as slash or AU.

POV - point of view. A story told from the point of view of one particular character.

songfic - A story built around the lyrics to a particular song, or inspired by it.

filk - Lyrics relating to fandom which are made up to the tune of songs we all know and love.

ABH - Anywhere But Here. A genre of fiction written in second person present tense, where the writer attempts to transport the reader into the shoes of the person who is telling the story and speak to the reader as though the choices are theirs. For example: You step into the room. Angel turns and stares at you, and he sees that you have bared your neck. His eyes darken. Blah, blah blah...it's a device that's generally badly used and not terribly respected.

ATG - Any Two Guys. A term used by slash writers to refer to a story in which the main characters display none of the unique characteristics that identify them, but instead could be any two men off the street thrown together. These stories are generic and show a lack of craft and skill on the part of the author; a search and replace on the character names would produce a story that could be any two guys.

OTP - 'One True Pairing'. This refers to the belief that a show supports only one pairing of characters that works within canon. Good examples would be Qui-Gon/Obi-Wan and Duncan/Methos. Usually, fans have a preferred OTP in their primary fandom, and can cite examples why they feel the particular pairing is the one they believe in strongly.

OOC -  'Out Of Character' One or several main characters have been written differently from canon.

Canon - The original material or source of the Fanfiction. Example- J.K Rowling's Harry Potter Books in this case.

Crossover- Another fan fiction subgenre is the crossover story, in which either characters from one story exist in (or are transported to) another pre-existing story's world, or more commonly, characters from two or more stories interact. An example would be the human refugee fleet led by the Battlestar Galactica finding and entering the territory of Star Trek's United Federation of Planets, or the characters from the television series CSI: Crime Scene Investigation solving crimes in the Harry Potter universe etc...

Drabble - is traditionally a story exactly 100 words in length. In fan fiction writing circles, many fandom's have a drabble community which sets a weekly prompt for authors to use in a drabble. A prompt can be a theme such as ‘faith’ or ‘mothers,’ a specific situation such as ‘someone is bleeding,’ an object, a line of poetry, an instruction such as ‘only dialogue,’ or ‘from the point of view of a minor character,’ etc.

No, I did not write this. The above is from  Destina's Fan Fiction website and Wikipedia.