This document defines and distinguishes between code switching and code mixing in bilingual communication. It explains that code switching involves changing languages unpredictably to fit the environment, and can occur between sentences or within a sentence. In contrast, code mixing involves borrowing words from one language into another without a change in topic, often within a single sentence. The document provides examples and discusses reasons for using code switching or code mixing, including lack of a word in one language, emphasis, or expressing group identity.