Ratings
Ratings taken from The Fanfiction Glossary.
An author- or archivist-applied system which lets readers know what they're in for before they start reading a story. Not all archives or mailing lists require ratings, but most of the good ones do -- ratings are increasingly becoming a solid component of good fanfic etiquette, and at very least authors are expected to warn readers if a story contains explicit adult content. Using the American movie guidelines as a template, most fanfic can be rated as follows:
:: G: Good clean fun for all ages.
:: PG: Mild implied sexual innuendo, mild bad words, or violence or serious (though not quite mature) topics.
:: PG-13: Some violence, bad language, obvious sexual innuendo, implied sexual relations. Also may include some mature topics such as suicide, homosexuality, drug/alcohol advocacy, rape aftermath, details of childbirth, etc. depending on the mores of the fandom involved.
:: R: Just-short-of-explicit sex, graphic torture or violence, rape. Not recommended for minors.
:: NC-17: explicit erotica, excessively gory violence. Often illegal for underage readers.