The Entertainment Software Ratings Board (ESRB) is an organization designed to control the suitability of video game content for children. There are 6 basic ratings.
eC-Early Childhood-Playable by all, but especially suitable for younger audiences.
E-Everyone-Suitable for all.
E10+-Unsuitable for persons under 10. Parental guidance is advised.
T-Unsuitable for persons under 13. Stricter parental guidance is advised.
M-Unsuitable for persons under 17. Nobody under this age may buy a game with this rating unless accompanied by a parent or adult guardian.
AO-Only suitable for adults. Nobody under 18 can buy a game with this rating.
An RP rating is added to games which have not yet earned a rating by the ESRB and is most commonly used in advertising. K-A was originally part of the group but was replaced with E in 1999. E10+ was added in late 2004 for games with too much mature content for E, but not enough to earn it a T rating.