Standard English. The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
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,