This document discusses language choice in multilingual communities. It defines key concepts like code switching, code-mixing, diglossia, bilingualism, and multilingualism. Code switching refers to alternating between two or more languages in discourse. Code-mixing incorporates elements of two languages within an utterance. Diglossia describes a situation where two language varieties are used differently in a community. Bilingualism is using two languages interchangeably, while multilingualism is the ability to communicate in three or more languages. The document also discusses language registers, styles, jargon, and slang.