#1
Standard English is the variety of English that is held by many to be 'correct' in the sense that it shows none of the regional or other variations that are considered by some to be ungrammatical, or non-standard English. Received Pronunciation, often called RP, is the way Standard English is spoken; without regional variations. Standard English and RP are widely used in the media and by public figures, so it has prestige status and is regarded by many as the most desirable form of the language.
http://www.usingenglish.com/glossary/standard-english.html http://www.usingenglish.com/glossary/standard-english.html]
#2
Examples and Observations:
"[Standard English is that] particular variety of English which is regarded by educated people as appropriate for most types of public discourse, including most broadcasting, almost all publication, and virtually all conversation with anyone other than intimates… . .
"Standard English is not entirely uniform around the globe: for example, American users of standard English say first floor and I've just gotten a letter and write center and color, while British users say ground floor and I've just got a letter and write centre and colour. But these regional differences are few in comparison with the very high degree of agreement about which forms should count as standard. Nevertheless, standard English, like all living languages, changes over time… .
"It is important to realize that standard English is in no way intrinsically superior to any other variety of English: in particular, it is not 'more logical,' 'more grammatical,' or 'more expressive.' It is, at bottom, a convenience: the use of a single agreed standard form, learned by speakers everywhere, minimizes uncertainty, confusion, misunderstanding and communicative difficulty generally."
(R.L. Trask, Dictionary of English Grammar. Penguin, 2000)
http://grammar.about.com/od/rs/g/standengterm.htm
#3
The variety of English that is generally acknowledged as the model for the speech and writing of educated speakers.
USAGE NOTE People who invoke the term Standard English rarely make clear what they have in mind by it, and tend to slur over the inconvenient ambiguities that are inherent in the term. Sometimes it is used to denote the variety of English prescribed by traditional prescriptive norms, and in this sense it includes rules and usages that many educated speakers don't systematically conform to in their speech or writing, such as the rules for use of who and whom. In recent years, however, the term has more often been used to distinguish the speech and writing of middle-class educated speakers from the speech of other groups and classes, which are termed nonstandard. This is the sense in which the word is used in the usage labels in this dictionary. But it should be borne in mind that when it is used in this way, the term is highly elastic and variable, since what counts as Standard English will depend on both the locality and the particular varieties that Standard English is being contrasted with. A form that is considered standard in one region may be nonstandard in another, and a form that is standard by contrast with one variety (for example the language of inner-city African Americans) may be considered nonstandard by contrast with the usage of middle-class professionals. No matter how it is interpreted, however, Standard English in this sense shouldn't be regarded as being necessarily correct or unexceptionable, since it will include many kinds of language that could be faulted on various grounds, like the language of corporate memos and television advertisements or the conversations of middle-class high-school students. Thus while the term can serve a useful descriptive purpose providing the context makes its meaning clear, it shouldn't be construed as conferring any absolute positive evaluation.