G - Suitable for children, no swearing, limited violence.
'G' means 'General Audience.' All ages admitted. This signifies that the fic rated contains nothing most parents will consider offensive for even their youngest children to read. Nudity, sex scenes, and scenes of drug use are absent; violence is minimal; snippets of dialogue may go beyond polite conversation but do not go beyond common everyday expressions.
PG - Mild language, limited sexual content, some violence.
'PG' means 'Parental Guidance Suggested.' Some material may not be suitable for children. This signifies that the fic rated may contain some material parents might not like to expose to their young children - material that will clearly need to be examined or inquired about before children are allowed to attend the fic. Explicit sex scenes and scenes of drug use are absent; nudity, if present, is described only briefly, horror and violence do not exceed moderate levels.
PG-13 - Stronger language, violence, sexual content.
'PG-13' means 'Parents Strongly Cautioned.' Some material may be inappropriate for children under 13. This signifies that the fic rated may be inappropriate for pre-teens. Parents should be especially careful about letting their younger children read. Rough or persistent violence is absent; sexually-oriented nudity is generally absent; some scenes of drug use may be described; one use of the harsher sexually derived words may be read.
R - Strong violence, harsh language, and sexual situations.
'R' means 'Restricted - Under 17 requires accompanying parent or adult guardian.' The story contains adult material, and parents are urged to learn more about it before letting their children read. An 'R' may be assigned due to a fic's use of language, theme, violence, sex or its portrayal of drug use.
NC-17 - Graphic violence and/or sex, and material of an adult nature.
'NC-17' means 'No One 17 and Under Admitted.' This signifies that the writer believes that most parents would feel that the fic is patently adult and that children age 17 and under should not be admitted to it. The fic may contain explicit sex scenes, an accumulation of sexually-oriented language, or scenes of excessive violence.