G - General Audiences.
All ages admitted. Nothing that would offend parents for viewing by children.

P - Parental Guidance Suggested.
Although no private parts of the body are exposed, may contain indecent postures, fetishes or sexually provocative.

R - Restricted.
Under 18 requires accompanying parent or adult guardian. Contains adult content such as female boobs, nudes or implicit private parts.

A - Adults Only.
No one 18 and under admitted. Contains explicit and clear private parts, sex scenes or BDSM.