This document defines sociolinguistics and discusses various aspects of language variation. Sociolinguistics is defined as the study of the relationship between language and society. It examines how people vary their language use across different social contexts and how language conveys social meanings. The document also discusses standard and non-standard language varieties, language variation in terms of both users and uses, and other types of language variation including dialect, register, accent, bilingualism/multilingualism, lingua franca, pidgin/creole, and code switching/mixing.