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.