This is probably a stupid question.
Whenever I hear people discussing movie ratings – the MPAA ratings system in the US, that is – quite often they say “GP” instead of “PG”. Why?
Because they don’t know what they’re talking about.
Seriously, I’ve never heard anyone say “GP.”
It means they’re older than you are.
Before the current G, PG, PG-13 and R system was in effect, they had a similar, but slightly less precisely codified movie rating system.
IIRC, you had G, for General audiences, GP, for General (with Parental Guidance), and M for Mature audiences.
At one time there was a GP rating. (Meaning “general patronage” but not exactly G rated).
When the system was initially started (1969?) the ratings were
G M R X
the ‘M’ meaning mature. This led to some confusion as some folks were led to beleive that a “Mature” movie was an adult film (or perhaps a film starring Victor Mature). 
To avoid this confusion the ‘M’ was changed to ‘GP’ which eveolved into ‘PG’
Later (due to the violence in the movie “Indiana Jones and the Temple of Doom”), a fifth category was added PG-13.
The ‘X’ category was changed to NC-17 because ‘X’ almost became synonymous with hardcore pornography.
Okay, this seems to be a good explanation of the history of the MPAA code:
http://www.mpaa.org/Ratings_history1.asp
According to the MPAA site, “GP” was only used for a year. Why does that term seem to have such staying power? I just saw someone on CNN talk about movie ratings, and use the term “GP-13”. It’s as if a slew of scientists are still talking about preventing and curing GRID.
I miss the X rating. It made movies sound so exciting. Who would be scandalized by a NC-17 rating for say Pink Flamingos?
Should be
E-everybody
T-teen and up 13-18
R-risque
The two are not completely identical. In order for a film to be officially rated, it must be submitted (for a fee) to the MPAA which has trademarked the ratings of G, GP, M, PG, PG-13, R, and NC-17. Only the MPAA can give out these ratings. But in order to quell complaints that the MPAA was forcing filmmakers to submit their films for review, the MPAA deliberately did not trademark the X rating. A film could be submitted to the MPAA and given an X rating (although now it would instead receive an NC-17 rating) or a filmmaker could decide to forego an MPAA review and simply give his film an X rating on his own. So an NC-17 rating means “the MPAA has reviewed this movie and rated it NC-17” and a current X rating means “the MPAA has never seen this movie”.
It always annoyed me that they took a simple system like “GMRX” and screwed with it.
Theu changed “M” to “GP”, I suspect because a lot of movie and theater companies thought the stigma of sex movies would rub off on them (they used to put “recommended for mature audiences only” on films with any risque content – even though, inthose pre-ratings days, they couldn’t show anything). So the ambiguous “GP” was born.
The problem was, a lot of parents thought it meant “General Patronage”, which lead to a lot of surprises. I remember one female comedian recounting how she took her son to see the GP-rated “The Hawaiians” (a sorta sequel to “Hawaii”), and being blindsided by the scene where Charlton Heston gets in a Japanese bath with the women. Toplessness abounded. Her theory is “GP” stood for “Get Popcorn”, which is what she told her son to do. (I saw the film when it came out, too. I wasn’t sent for popcorn.)
So they changed it to “PG”, which was intended, apparently, to stand for the unambiguous “Parental Guidance”.
Note, too, that the logos for MPAA ratings are all in boxes, while the X-rating is in a circle. This was also a way to indicate that X meant the MPAA did not rate the film, and that anyone could rate their film X.