Bilingualism is the ability to speak and understand two or more languages. Multilingualism is the ability to speak and understand three or more languages, and polyglottism is the ability to speak and understand many languages.

Simultaneous bilingualism is the ability to speak and understand two or more languages from birth or early childhood. Sequential bilingualism is the ability to speak and understand a second language after the first language has been acquired.

Language attrition is the loss of one language while acquiring another. Language shift is the process by which one language replaces another as the dominant language in a community. Language death is the process by which a language ceases to be spoken by any living person. Language replacement is the process by which one language is replaced by another in a community.

Bilingualism has been shown to improve executive function, enhance memory, and increase creativity.

Bilingualism can increase job opportunities, enhance cultural understanding, and strengthen social ties.

Bilingualism can present challenges such as language interference, code-switching, and accent.

Code-switching is the use of two or more languages in a single conversation. Language mixing is the combination of two or more languages into a new language. Language blending is the process of merging two or more languages into a single language. Language alternation is the use of two or more languages in different contexts.

Passive bilingualism, receptive bilingualism, and comprehension bilingualism all refer to the ability to understand a language without being able to speak it.

Active bilingualism, productive bilingualism, and expressive bilingualism all refer to the ability to speak a language without being able to understand it.

Balanced bilingualism, coordinate bilingualism, and ambilingualism all refer to the ability to speak and understand two or more languages with equal proficiency.

Imbalanced bilingualism, asymmetrical bilingualism, and differential bilingualism all refer to the ability to speak and understand two or more languages with different levels of proficiency.

Language mixing, language blending, and language fusion all refer to the use of two or more languages in a single word or phrase.

Code-switching, language alternation, and language mixing can all refer to the use of two or more languages in a single sentence.

Language mixing, language blending, and language fusion can all refer to the use of two or more languages in a single text.

Code-switching, language alternation, and language mixing can all refer to the use of two or more languages in a single discourse.