1. pidgins and creoles

Throughout history no natural language is pure or free from the influence of other languages. Due to trade, war, colonization and other causes languages may come into contact. When this occurs, mixed codes may come into being, which are called pidgins and creoles. 

1) The term pidgin is the label for the code used by people who speak different languages. A pidgin is not the native language of any group. Pidgins are mixed languages that are simplified syntactically and lexically.

2) A creole is a mixed language which has become the mother tongue of a speech community. Creoles are not confined to certain functions of language nor reduced in syntax and lexis.

2. Bilingualism and multilingualism

Bilingualism and multilingualism are normal in many parts of the world today. Monolingualism, bilingualism or multilingualism is the result of language planning. Some people grow up speaking two languages because their family is bilingual. This situation is termed coordinate bilingualism. Others have to learn a second language as they grow up. This kind of bilingualism is called subordinate bilingualism.

Bilingualism gives rise to code-switching and code-mixing. The former refers to the fact that a speaker changes from one language to the other in different situations or when talking about different topics. The latter refers to the change from one language to the other language within the same utterance.