The MPAA guidance on the PG moving rating is that some of the content in the film may not be "suitable" for younger audiences. The MPAA assigns a movie with a PG rating when it contains some profanity, some violence or brief nudity of a "nonsexual" nature.
In an effort to refine the rating system and find an intermediate rating between the PG and the R (restricted) rating, the MPAA added the PG-13 rating in 1984. As the MPAA notes, "a PG-13 rating is a sterner warning by the Rating Board to parents to determine whether their children under age 13 should view the motion picture."
Prior to 1984, a film that depicted any drug use at all was given an R rating. Since the PG-13 rating was adopted, drug use featured in a motion picture requires at least a PG-13 rating. Drug abuse calls for an R rating. Additionally, a PG-13 movie may have some violence, as long as the violence is neither "persistent" nor "realistic and extreme."
The MPAA rates a film PG-13 when it contains one harsh "sexually derived word used as an expletive." If two words are used, or one such word is used in a "sexual context," the MPAA gives the film an R rating.
More than brief nudity that is not sexually oriented calls for a PG-13 rating. Sexually oriented nudity gives the film a higher rating of R and possibly NC-17.
The Rating Board reserves the right to rate a movie PG-13. The criterion stated by the MPAA specifies that if two-thirds of the Raters "feel that most American parents would believe that a PG-13 rating is appropriate" due to content, the movie is rated PG-13.