G and PG are the ratings for movies and TV programs promulgated by the Motion Picture and TV people to pretend that they care how corrupted the youth of America (the US) are.

G = General Audiences (all ages admitted)
PG = Parental Guidance Recommended (ask your mommy)

I believe the "R" rating, Restricted, is still used to mean no one under 18(?) admitted (sometimes with "unless accompanied by an adult"), and in some places "X" or "XXX" means "please don't enter if you're under age since they'll send the operator to jail if you get caught."

The terms are used generically for all kinds of literature, art, situations - (but not always favorably and sometimes sarcastically?)

John