The age classification of a film
in the UK. See: U
The classification is legally binding. Ie, the cinema, or video retailer can be prosecuted if they let someone under that age see the film or video.
For a film (or video programme) to be released on video, it must (by law) be certified by the BBFC as being suitable for persons above a specific age, or as being suitable for all viewers. Films at cinemas needn't necessarily be certified by the BBFC; they can be given a local authority certificate instead, but this is only done with a few art house films. There are different rules for film societies as well. If the BBFC denies a film a certificate, it is in effect, banned from video release. There's different standards for film and video releases too. A film may be certified for one age at the cinema, but a different age on video, or may be denied a video certificate altogether (because videos have pause buttons. :)
The certificate is shown before the film in cinemas. In the olden days, they used to also have to hang a copy of the certificate outside the cinema.
Before some time in the early 80s, the certificates were U, PG, A, and X.