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Received Pronunciation (RP) is a form of pronunciation of the English language which has been long perceived as uniquely prestigious amongst British accents and is the usual accent taught to non-native speakers learning British English.
The earlier mentions of the term can found in H. C. Wyld's A Short History of English (1914) and in Daniel Jones's An Outline of English Phonetics, although the latter stated that he only used the term "for want of a better".

Usage
Except in the last bastions of "real" RP use, the pronunciation has in fact changed over time. For instance, foreigners learning their English accents from Royal speeches would find they are looked at very strangely in the streets of Britain, because the Queen's "speech voice" has changed little since the 1950s, and now sounds archaic even to most people who would consider that they speak "correctly" (i.e. RP).
The change in RP may even be observed in the home of "BBC English". The BBC accent from the 1950s was distinctly different from today's: a news report from the '50s is instantly recognisable as such, and a mock-1950s BBC voice is often used for comic effect in TV or radio programmes wishing to satirize outdated social attitudes such as the Harry Enfield Show and its "Mr. Cholmondeley-Warner" sketches.

Changing status of Received Pronunciation
Traditionally, Received Pronunciation is the accent of English which is "the everyday speech of families of Southern English persons whose menfolk have been educated at the great public boarding schools" (Daniel Jones, English Pronouncing Dictionary, 1926—he had earlier called it "Public School Pronunciation"), and which conveys no information about that speaker's region of origin prior to attending the school.
It is the business of educated people to speak so that no-one may be able to tell in what county their childhood was passed.
A. Burrell, Recitation. A Handbook for Teachers in Public Elementary School, 1891.
For many years, the use of Received Pronunciation was considered to be a trait of education. It was a standard practice until around the 1950s for university students with regional accents to modify their speech to be closer to RP. As a result, at a time when only around five percent of the population attended universities, elitist notions sprang up around it and those who used it may have considered those who did not to be less educated than themselves. Historically the most prestigious British educational institutions (Oxford, Cambridge, many public schools) were located in England, so those who were educated there would pick up the accents of their peers. (There have always been exceptions: for example, Morningside, Edinburgh and Kelvinside in Glasgow had Scottish "pan loaf" accents aspiring to a similar prestige.)

Traditional status
From the 1970s onwards, attitudes towards Received Pronunciation have been slowly changing. One of the primary catalysts for this was the influence in the 1960s of Labour prime minister Harold Wilson. Unusually for a recent prime minister, he spoke with a strong regional Yorkshire accent, exaggerated, some said, to appeal to the working classes his party represented.
As a result of the trend begun by Wilson and others during the 1960s, the accents of the English regions and of Scotland, Wales, and Ireland are today more likely to be considered to be on a par with Received Pronunciation. BBC reporters no longer need to, and often do not, use Received Pronunciation, which in some contexts may sound out of place, and be discouraged in favour of less "cultivated" accents.

Changing attitudes

Phonology
A table containing the consonant phonemes is given below

Consonants
The vowel phonemes of Received Pronunciation are shown in the following tables:
Examples: /ɪ/ in kit and mirror, /ʊ/ in foot and put, /ɛ/ in dress and merry, /ʌ/ in strut and curry, /æ/ in trap and marry, /ɒ/ in lot and orange, /ə/ in the first syllable of ago and in the second of sofa.
Examples: /iː/ in fleece, /uː/ in goose, /ɜː/ in nurse and bird, /ɔː/ in north and thought, /ɑː/ in father and start.
RP's long vowels are slightly diphthongised. Especially the vowels /iː/ and /uː/ which are often narrowly transcribed in phonetic literature as diphthongs [ɪj] and [ʊw].
Although these vowels are traditionally described as long vowels, whereby they have received the <ː> mark after their symbol, the length also varies according to the surrounding sounds. If a long vowel is preceded by a voiceless consonant sound (e.g. /p k s/) its length will be equivalent to that of the short vowels, with the exception of /ɑː/ which becomes halfway between long and short. e.g. Burt = [bɜt], seat = [sit], garth = [gɑˑθ].
The short vowel /æ/ becomes longer if it is followed by a voiced consonant sound. Thus, in narrow transcription bat = [bæt] and bad = [bæːd]. In natural speech, the plosives /t/ and /d/ may be unreleased utterance-finally, thus distinction between these words would rest mostly on vowel length.
Examples: /ɪə/ in near and theatre, /eɪ/ in face, /ɛə/ in square and Mary, /əʊ/ in goat, /aɪ/ in price, /aʊ/ in mouth, /ɔɪ/ in choice, /ʊə/ in tour.
The off-glide of /eɪ/ (and also the off-glides of /ij/ and /uw/) can be predicted by a phonological rule and so are not represented in some underlying representations.
There are also the triphthongs /aɪə/ as in fire and /aʊə/ as in tower. The realizations sketched in the following table are not phonemically distinctive, though the difference between /aʊə/ /ɑɪə/ and /ɑ:/ may be neutralised under [ɑ:] or [ä:]
Not all reference sources use the same system of transcription. In particular
Most of these variants are used in the transcription devised by Clive Upton for the Shorter Oxford English Dictionary (1993) and now used in many other Oxford University Press dictionaries.

/æ/ as in trap is often written /a/.
/e/ as in dress is often written /ɛ/.
/ɜː/ as in nurse is sometimes written /əː/.
/aɪ/ as in price is sometimes written /ʌɪ/.
/aʊ/ as in mouse is sometimes written /ɑʊ/
/ɛə/ as in square is sometimes written /eə/, and is also sometimes treated as a long monophthong /ɛː/. Vowels

Unlike most forms of English English and American English, RP is a broad A accent, so words like bath and chance appear with /ɑː/ and not /æ/.
RP is a non-rhotic accent, meaning /r/ does not occur unless followed immediately by a vowel.
Like other accents of southern England, RP has undergone the wine-whine merger so the phoneme /ʍ/ is not present.
RP uses [ɫ], called dark l, when /l/ occurs at the end of a syllable, as in well, and also for syllabic l, like in little or apple. (whereas it has been reported Historical variation

Accent (linguistics)
Prestige dialect
English English
Estuary English
General American
Prescription and description
Cockney