This document summarizes the different film rating systems in the UK. It explains that a U rating means a film is suitable for all ages 4 and over and may contain mild themes or language. A PG rating means parental guidance is advised as scenes may not be suitable for young children, and may contain mild bad language. Films rated 12A are not suitable for those under 12 without an adult, while a 15 rating means no one under 15 can view the film. An 18 rating restricts viewing to adults only due to strong content like violence or sex. The most restrictive R18 category is only for explicit adult films shown in licensed venues.