New words, hip hip! Multilingualism, hooray! Multilingual puns! *faints from nerdiness*
Macaronic refers to text spoken or written using a mixture of languages, sometimes including bilingual puns, particularly when the languages are used in the same context (as opposed to different segments of a text being in different languages). The term is also sometimes used to denote hybrid words, which are in effect internally macaronic. A rough equivalent in spoken language is code-switching, a term in linguistics referring to using more than one language or dialect in conversation.
Macaronic Latin specifically is a jumbled jargon made up of vernacular words given Latin endings, or for Latin words mixed with the vernacular in a pastiche (compare dog Latin).
The word macaronic comes from the New Latin macaronicus, from Italian dialect maccarone (“dumpling, macaroni”, regarded as coarse peasant fare). The term macaronic has derogatory overtones, and it is usually reserved for works where the mixing of languages has a humorous or satirical intent. It is a matter of debate whether the term can be applied to mixed-language literature of a more serious nature and purpose.