A G-rated movie is suitable for all ages. It contains no objectionable content and can be viewed by small children.
PG stands for "parental guidance suggested." PG films are a little more intense than G films and may contain some mild violence.
PG-13 means that parents are strongly cautioned against letting kids younger than 13 see the film. It may contain action-style violence, erotic situations or a handful of swear words.
R stands for "restricted." An R-rated film contains adult themes, violence and/or nudity; anyone under 17 who wishes to see it must be accompanied by a parent.
NC-17 movies are meant solely for adults. No one under 17 may attend them under any circumstances.