(Many of these definitions have been written with tongue firmly planted in cheek, so while all the definitions are technically correct, they will also have my own unique spin on them.)
blog: 1. short for weblog; an internet based journal of any source 2. used as a verb [to blog] meaning to write and publish an entry to an internet based journal.
fanfic: short for fan fiction; stories of any length written about pre-existing characters and situations as defined by popular (or not so popular) books, television shows, movies, etc.
[Author's Note: My most recent discovery is fan fiction for Dorothy Sayers' Lord Peter Wimsey mysteries and The Odyssey. Yes, the one by Homer. There is fanfic for EVERYTHING. Quite amusing.]
fandom: used to describe the community of fanfiction readers and writers
comment / review: a message left by a reader for the author of a particular blog and/or piece of fanfiction. Comments and reviews make the author feel loved and are often accompanied by warm fuzzy feelings, except in the case of flames (see below). Lack of comments and/or reviews when the author KNOWS that her family and friends read the blog/fanfic can often result in low self-esteem and lots of annoying begging for comments. You have been warned.
flame: a negative review; more than that, however, a flame is generally left anonymously, and is frequently vituperative, if not ridiculous. The commenter who called me a "bloody twelve-year old" because I gave one of my characters dyed pink hair would count as a flamer or writer of a flame.
beta reader: usually shortened to just beta; someone who reads over a piece of fic before it gets publically posted; an editor; used as a verb [to beta] to describe the editing process; from the idea that the author would be the alpha, or first reader, and the beta would be someone who takes a second look.
brit picker: (possibly unique to Harry Potter fandom) a native of the British Isles who reads over a story to correct the author's British slang, phraseology, and spelling.
[Who knew that Brits don't use the word "gotten" -- it's baffling.]
meme: usually a series of questions that reveal something about the author's personality which tend to get passed around on the internet; of uncertain origins.
gack: to steal; "I gacked that meme from Allison." "Feel free to gack these icons."
drabble: a 100 word story; double-drabbles, then, would be 200 words. [The definition of drabble is highly contested in fandom. Some claim that the only true drabbles are exactly 100 words -- the length requirement being part of the challenge of writing them. Others insist that any short piece (say, under 500 words) qualifies as a drabble. The controversy rages on.]
ficlet: a short (usually around 500-1000 words) piece of fanfiction
canon: a fact which is spelled out specifically in the source material for the fanfiction. (ie: The fact that Harry Potter is in Gryffindor house at Hogwarts is canon.)
fanon: a fact which is NOT specifically stated in the source material, but is generally believed to be true by the fandom (ie: the fact that Lily Potter was in Gryffindor house is not specifically stated in any of the Harry Potter books, but fans generally believe it to be so.)
ship: short for relationship; refers to the relationship featured in a particular story
[Readers and Authors alike are extremely picky about which "ships they sail," meaning which relationships they like to read or write about. There are canon ships, fanon ships, and squick ships. It's mind boggling.]
slash: fiction written about homosexual relationships; the origin of the term is from fanfiction writers who included the relationship they were writing about with a slash between the characters, (ie: Alexander/Hephestion)
Mary Sue: a character in a fanfic who is a bad cliche; generally refers to characters who are TOO perfect, who have no flaws, and are therefore unbelievable; also refers to bad portrayal of canon characters, ie: Hermione-Sue; male form is Gary Stue.
shoutbox: a miniature message board placed on a blog for the purpose of "chatting" with other readers of the blog. See Allison's Blog for an example.
A/N: abbreviation for Author's Note; usually included at the beginning or end of a piece of fan fiction and/or an individual chapter; a place for the author to speak directly to the reader
ratings: based on the MPA system for rating films, fan fiction is rated based on it's content and suitability for general audiences. From G all the way to NC-17. Really.
fangirl: a person (regardless of gender) who becomes incomprehensible and loses all understanding of grammar and spelling when he/she encounters something they feel passionate about.
[ie: "OMG!!!!!!!1!!! UR the COOLST! i LUV THIS FIC!!!!!!!!!]
OMG: short for "oh my god"
LOL: short for "laughing out loud"
ROTFL: short for "rolling on the floor laughing"
[Seriously. I didn't make these up.]
*: generally used to indicate an action as in, *sigh* or *facepalms*
avitar: a small picture used on message boards to identify a user (also sometimes known as icons)
meta: discussion of anything deeper or broader than the average fandom conversation; ie: a discussion about the literary aspects of fandom, the larger social forces behind the movement, the technical side of writing, etc.
dork: anyone who takes the time to actually compile a list of fandom/blog/internet jargon; anyone who reads the list all the way to the end. ;c)