In sociolinguistics, a variety, also called a lect, is a language or dialect considered as a variety or development of another language or dialect. It is often as a way of avoiding the terms 'language' and 'dialect' in intermediate cases (say of some but low mutual intelligibility) where it is difficult to objectively decide whether two speech communities should be classified as separate languages or as dialects of one language, or where the language-defining criteria of mutual intelligibility and ethnic identity conflict, as in Serbian and Croatian (mutually intelligible but ethnically distinct) or Mandarin and Cantonese (unintelligible but ethnically unified).
The term "lect" is a back-formation from specific terms such as dialect and idiolect.
Special examples of lects include:
Varieties such as dialects, idiolects, and sociolects can be distinguished not only by their vocabulary, but also by differences in grammar, phonology and prosody. For instance the tonal word accents of Scandinavian languages have differing realizations in many dialects. As another example, foreign words in different sociolects vary in their degree of adaptation to the basic phonology of the language.
Certain professional registers such as legalese show a variation in grammar from the standard language. For instance English journalists or lawyers often use grammatical moods such as the subjunctive or conditional mood, which are no longer used frequently by other speakers. Many registers are simply a specialised set of terms (see technical terminology, jargon).
It is a matter of definition whether slang and argot are to be considered included in the concept of variety or of style.Colloquialisms and idiomatic expressions are usually understood as limited to variation of lexicon, and hence of style.