What Is Standard English?

Standard English, also known as Standard Written English or SWE, is the form of English most widely accepted as being clear and proper.

Publishers, writers, educators, and others have over the years developed a consensus of what standard English consists of. It includes word choice, word order, punctuation, and spelling.

Standard English is especially helpful when writing because it maintains a fairly uniform standard of communication which can be understood by all speakers and users of English regardless of differences in dialect, pronunciation, and usage. This is why it is sometimes called Standard Written English.

There are a few minor differences between standard usage in England and the United States, but these differences do not significantly affect communication in the English language.

from Common Errors in English Usage ~

What is an error in English?
The concept of language errors is a fuzzy one. I'll leave to linguists the technical definitions. Here we're concerned only with deviations from the standard use of English as judged by sophisticated users such as professional writers, editors, teachers, and literate executives and personnel officers. The aim of this site is to help you avoid low grades, lost employment opportunities, lost business, and titters of amusement at the way you write or speak.