BBFC is a an organisation that rates the age rating for movies and TV programs. This is British rating system. its a non profit organisation that aims to regulate everything correctly.
U- Means everyone can watch it, it is Universal for children 4+. anyone under 4 it will be a specific label instead of U. There might be Kissing/cuddling but there will not be any sexual jokes. Violence wont be used in the movies but there might be action scenes. Its subtle movies and quite calming
PG- Parental guidance;. Unlikely sex references, if there are ones then little children wont understand. Mild swearing such as shit could be said but less likely. No real gore you just see an imply wound shown or maybe a little splatter of blood.
12A/12- the A represents Adult so you cant watch them without being with an adult and you can be any age aslong as you are with an adult. Strong language such as Fuck can be used and sexual jokes and imply sexual scenes can be used but to a certain degree
15- Strong violence and sexual activities are allowed, sexual nudity and drug taking can be shown. Discrimination language and behaviour can be allowed. In 15 can get away with a lot more than they used to be so sexual activities in movies can be shown and a lot of gory violence can be used.
18- Extreme gore, Extreme language and Extreme sexual content. Majority is allowed but there is a point of extremity where it can not be allowed
R18- Pornographic imagery and gore and yeah...
Elephant
http://www.bbfc.co.uk/case-studies/elephant
This is a 15 due to the amount of bad language is used through out the movie as this movie is based on the leading up to a school shooting but told by multiple perspectives.