A dialect is a form of the language that is spoken in a particular part of the country or by a particular group of people. There are many different dialects of English and they have different words and grammar. Most learners of English learn the standard dialects of the language.
There are many different forms of standard English: for example, standard British English, standard American English, standard New Zealand English, standard Indian English. The standard dialects of the language are used by governments, in the media, in schools and for international communication.
A dialect is not the same as an accent. An accent refers to the way we pronounce words and the standard dialect of a language can be spoken with different accents.
Examples of dialect forms in British English are:
I ain’t going to school today. (standard form: I’m not going to school today.)
She don’t understand. (standard form: She doesn’t understand.)
Would you like a cheese cob? (cob is a dialect word in parts of the north of England and means ‘bread roll’.)
Standard dialects are not better than other dialects, but we don’t use dialect words or grammar in an essay, during an interview or in other formal contexts.