Received Pronunciation (or RP, or BBC English) is the name given to the standard accent of English used by the British Broadcasting Corporation. It is used most often in the south of England, and by some people all over Britain. It is more often called Standard English.
Foreign students of British English learn this kind of English at school. The British pronunciation of words given in dictionaries is in Received Pronunciation. Received Pronunciation is used because the 20th century saw the coming of radio and television. Before then, regional dialects were more used. Education beyond elementary level was not available for most people. Schooling ended at 12 in 1910, and at 14 as late as 1950. Until about 1960 in England, most people lived near where they were born. Regional accents were strong in the West and North of England.
Received Pronunciation is non-rhotic. This means that in words ending with an 'r', for example car, the final 'r' is not pronounced. Many words have long vowel sounds. For example, the 'a' in 'bath' rhymes is the same as in 'far', not the same as in 'cat'.