This document discusses the UK film classification system. It explains that a 'U' rating means films are suitable for all ages over 4 and should have a positive message. A 'PG' rating means general viewing but some scenes may not be suitable for young children. Films rated '12A' and '12' are generally suitable for those over 12 but may upset younger viewers. Only those over the age of 15 can see a '15' rated film. An '18' rating means only adults 18 and over can view the film. The 'R18' classification is for explicit adult films that can only be viewed by adults in licensed establishments.