ESRB ratings are based on several content areas that include violence, sex, language, substance abuse, and humor. Ratings come in two parts. One of five rating symbols indicating the perceived appropriate age group for the game is marked on the front of each game: EC (Early Childhood), E (Everyone), T (Teen), M (Mature), or AO (Adult Only). In addition, content descriptors listed on the back of each game box explain exactly what elements consumers should be concerned about.
For more information on video game ratings, visit the ESRB web site: http://www.esrb.org/index.asp