This document introduces the concepts of language variation, dialects, and sociolects. It defines dialects as geographical variants of a language that are mutually intelligible, differing in phonology, syntax, and lexicon between regions. Sociolects refer to linguistic differences between social groups. Language naturally varies across both time and space in dialects and across social dimensions in sociolects. Variation exists within and between speakers and groups, and linguistic forms can be adopted from other dialects or sociolects to perform identity.