Warnings
Angst
Refers to emotional anguish/torment/etc. suffered by a character.
Anthro - anthropomorphic/furries/furry/plushy/plushophiles
An animal with human-like characteristics. A human with animal-like characteristics can also be called an anthro.
BDSM - bondage/discipline/sado-masochism
Consensual sexual relations involving: sexual slavery, master/slave relationships, sadism and masochism, bondage games, kinks and fetishes. Props may include leather, whips, chains, etc.
Bestiality
Sexual relations between a human and an animal.
Character Death
A story in which one or more major characters dies.
D/s - dominance/submission
Deals with Dominance/submission issues, usually with consent implied.
H/C - hurt comfort
A type of story in which one character is harmed (emotionally/physically) and is saved by another, who then makes them feel better/protected/etc.
Het - heterosexual
A story depicting a romantic or sexual relationship between a male and a female.
Incest
Sex between two people so closely related by blood (e.g. within the nuclear family) that the law would forbid marriage between them.
Lemon
A label used to describe a story with graphic sexual content.
Lime
A label used to describe a story with non-explicit sexual content.
MPreg - male pregnancy
Describes a story involving male pregnancy - by whatever means the author chooses.
N/C - non-consensual
A label used to describe a story that contains forced sex or rape.
Necrophilia
Erotic attraction to or sexual contact with corpses.
Pre-slash
A story that explores the potential for a same-sex relationship without the characters actually getting together.
PWP - porn without plot
Generally refers to a fanfiction in which nothing occurs but steamy, graphic sexual scenes.
Shotacon
A romance story (usually, but not always sexual in nature) in which at least one of the participants is a young boy. The age cut-off is about 15.
Shounen-ai
A label for stories which deal with sweet, non-graphic romance between two guys, a milder term than yaoi.
Slash
A label that implies a homosexual relationship between two characters from a series.
Spoiler(s)
A piece of information which can reveal (and thereby "spoil") an important plot point in a series that the reader has not yet seen/read.
Squick
To be "squicked" is to have been disturbed at a personal gut level, often but not always in regards to sex.
Suicide/Suicidal Themes
Generally refers to a story that depicts a person who intentionally takes his or her own life.
Tentacles
Any erotic tale involving characters or monsters who use tentacles (often phallic) to mate with or simply molest a humanoid character with.
Violence
Graphic scenes of violence are present in the story and is not for the faint hearted.
Yaoi
Indicates stories dealing with male/male (gay) pairings, usually for adults only - the Japanese version of hardcore slash.
Yuri
Indicates stories dealing with female/female (lesbian) pairings, usually intended for adults only - the male equivalent is yaoi.

