Welcome to Gaia! ::

People love to abbreviate things and I have noticed that some groups love to come up with random terminology that only they understand or something that makes them superior to others in some way. Just ignore them, their not right in the head wink hehe

Here are, generally, the most important/well known ones:

Fandom: Any TV show, book, movie, comic, series, etc. Basically anything you can be a fan. A fandom is a group of fans who like the same thing.
Fanfic: short for fanfiction, a work of fiction created by a fan
Con crit: Constructive Criticism
R&R: read and review

A/N: Author's Notes
Drabble: fic of a hundred words or less (generally applied to any fic shorter than 500 words)
One-shot: One chapter fic, not planned to continue
Two-shot: Two chapter fic, not planned to continue
Short Story: less than 17,500 words
Novella: less than 50,000 words
Novel: 50,000 words+
Epic Novel: 100,000 words+
WIP: work in progress
Canon: Anything that appeared in the published work the fandom is based on.
AU: Alternate Universe
RPF: Real Person Fic, a fic about a real person who is living or has lived (or perhaps a future relative)
H/C (Hurt/Comfort): one character is harmed, the other comforts
Fluff: light-hearted romance, many 'feel-good' moments
Shipping: Relationshipping; pairing characters together
Slash: Gay pairing, typically MxM
Femslash: A gay pairing that is specifically FxF

IC: in character
OOC: Out Of Character
CC: Canon Character
OC: Original Character
Mary Sue: Original Character that does not fit into the fandom, warps the fandom around her, or otherwise is not believable in the context of the fandom and the fic. (A character who can fly in a world where flying is not possible, etc). A character whose weaknesses do little to nothing to balance with their usually many strengths.
Gary Stu: See Mary Sue; male version of a Mary Sue
Canon-Sue: A character in the canon who happens to be a Sue.
Self-Insert: Original Character that is, in a way, the author's avatar within the fic. Not always a Mary Sue.

Other fairly common stuff:
Crackfic: a fic where everyone acts OOC and nothing really makes sense
Flame: A review, post, or PM that insults an author and possibly the story, no matter the reason. Generally viewed as unwarranted.
Ship war: A war between two followings of different 'ships, usually sharing one common character, thus the reason for their fighting. (HarryxHermione vs RonxHermione)
Name-splicing: A crossing of two character's names, generally the aggressor of the relationship is put first. Ex: Hermione seducing Severus Snape: Hermape. Snape seducing Hermione: Snapione.
Citrus: Sexually explicit scenes or fics (generally assumed to have no plot beyond the sex)
Lemon: Sexually explicit; descriptive, though not overly so; usually rated M (generally assumed to have no plot beyond the sex)
Lime: Sexually explicit; vaguely descriptive; mostly implied; usually rated T (generally assumed to have no plot beyond the sex)
PWP: Plot, what plot? or Porn without plot; usually a pairing oriented one-shot, featuring two characters sleeping together without any explanation.
Incest: Within the family pairings
Twincest: Pairing twins
MPREG: male pregnancy
Shonen-ai: Japanese gay pairing; male (non-sexual)
Shoujo-ai: Japanese gay pairing; female (non-sexual)
Yaoi: Japanese gay pairing; male (sexual)
Yuri: Japanese gay pairing; female (sexual)