Synopsis: The reading unit features varieties of the English language used affected by gender differences, social contexts, register, geographical factors and scale of formality in spoken and written forms, those of which are sociolinguistic factors all language learners should master.
A language variety is a sub-set of formal features which correlates regularly with a particular type of socio-situational feature. When we talk about Mr. X's English or Miss Y's English we are referring to different users of English.
Contrasts and comparisons between British and American English, on the other hand, indicate that the place in which we learnt and use English is reflected in what we speak and write. Geographical dialects are the related categories.
In the 1950s an attempt was made to distinguish between U and non-U English that is Upper Class and Non-Upper Class English. Such distinctions reflect the relationship between language and social class.
There remains another type of dialect distinction which worth taking into notice. is This is the distinction between the language used by males and that by females, or language and gender differences.