Adventure: A fictional genre involving action, danger, and unknown risks.
Angst: A fictional genre in which one or more of the characters suffers emotional and sometimes physical torment.
AU: Alternate Universe. This term either refers specifically to the HTLJ eps, Stranger in a Stranger World and Stranger and Stranger, or fan fic set outside the show's usual timeline.
BDSM: Bondage, Dominance, Sadism, Masochism. Sometimes broken down into component parts.
Comedy: A story of light and amusing character and typically with a happy ending.
DD: Domestic Discipline. Refers to a relationship between two people in which one is a disciplinarian, the other the disciplined--but not in a sexual context (if it's sexual, it's called D/s).
Drama: A story intended to portray life or character, usually involving conflicts and emotions through action and dialogue.
D/s: Domination/submission. Cf. DD.
G: A North American film rating, indicating content (sex, violence, language) inoffensive to pratically anyone. (See How Stuff Works for more information.)
Gen: Variously meaning 'general', 'generic.' Essentially refers to fic that does not depict sexual relationships, either slash or het.
Het: Fic where the primary relationship between characters is heterosexual. May contain a relationship between a media figure and an OC.
HC: Hurt/Comfort. Genre where one character suffers pain, usually physical (sometimes rape), and is then tended to by another. Sometimes leads to sex.
Incest: Sexual relationship involving closely related characters.
Kink: Can include any number of non-vanilla sexual practices such as BDSM, DD, D/s, scat, water sports, etc.
Mary-Sue: An original female character who is idealized ad nauseum by her author. Her appearance and behavior are cliched. Sometimes used to describe OMCs, although the term there is sometimes Herkie-Sue or Marty-Sue.
M-Preg (mpreg): Male pregnancy. Stories with a male who becomes pregnant, with the accompanying physical changes (lactation, birth).
N/C: Non-Consensual. Term used for fic depicting rape or problematic sexual consent in general.
N/C issues: Non-Consensual issues. Lesser degree of N/C; consent may be murky, but not outright rape.
NC-17: A North American film rating, indicating explicit sexual content (not related to NC). (See How Stuff Works for more information.)
OFC: Original Female Character. This is a character invented by the author, and is often associated with Mary-Sue.
OMC: Original Male Character. This is a character invented by the author, and is often associated with Marty-Sue.
Ongoing: An unfinished story.
PG: A North American film rating, indicating content of mild violence or profanity and non-explicit sex. (See How Stuff Works for more information.)
PWP: Plot? What Plot? Stories where the emphasis is solely on sex. Usually, they don't display much development.
R: A North American film rating, indicating non-explicit sexual content. (See How Stuff Works for more information.)
Romance: A fictional genre focusing on the development of the relationship of two (occasionally more) characters; a love story.
Scat: Sexual play involving feces (abbr. of scatology).
Slash: Fic playing up perceived homoerotic overtones in various cultural media. Named after the punctuation mark '/' initially used to separate Kirk/Spock, the first 'official' slash pairing.
Uber: This term is specific to the Xenaverse, and is essentially equivalent to the AU genre. It refers to a story set beyond the show's usual timeline.
Underage: Sexual relationship involving a minor.
Vignette: A short piece, usually around 3 pages, that deals more with character, etc. than plot.
Water Sports: Sexual play involving urine.
X-Over: Crossover. A fic that unites characters from two shows (in this fandom, we tend to treat HTLJ and XWP as one show).