To answer your question, Lee:
The current MPAA movie ratings consist of:
Rated G – GENERAL AUDIENCES: All ages admitted.
Rated PG – PARENTAL GUIDANCE SUGGESTED: Some material may not be suitable for children.
Rated PG-13 – PARENTS STRONGLY CAUTIONED: Some material may be inappropriate for children under 13.
Rated R – RESTRICTED: Under 17 requires accompanying parent or adult guardian.
Rated NC-17 – No one 17 and under admitted.
X or XXX is still used by the adult industry but is not regulated by MPAA
If a film was never submitted for a rating, the label "NR" (Not Rated) is often used, however "NR" is not an official MPAA classification.
Film that have not yet received MPAA classification are advertised under the banner, "This film is not yet rated".