A rating usually given to movies or television shows, to indicate the type of content, and to which audience it is suited for.
Usually used to denote a move/show that contains course language, violence, nudity, and sex.
It should be noted, that the sex shown is of a non penetrative kind, though it may be explicitly implied. It is not shown.
As well, the nudity may include frontal nudity, but does not show a fully aroused male genitals.
Originally developed by the movie industry to stave off Government regulations.