Language contact occurs when speakers of two or more languages or varieties interact and influence each other. The study of language contact is called contact linguistics. When speakers of different languages interact closely, it is typical for their languages to influence each other. Language contact can occur at language borders, between adstratum languages, or as the result of migration, with an intrusive language acting as either a superstratum or a substratum. Language contact occurs in a variety of phenomena, including language convergence, borrowing and relexification. The common products include pidgins, creoles, code-switching, and mixed languages. In many other cases, contact between speakers occurs but the lasting effects on the language are less visible; they may, however, include loan words, calques or other types of borrowed material. Multilingualism has been common throughout much of human history, and today most people in the world are multilingual. Methods from sociolinguistics (the study of language use in society), from corpus linguistics and from formal linguistics are used in the study of language contact. Locus of diffusion It is easy to see how a word can diffuse from one language to another, as borrowing a vocabulary item from one language to introduce into another language is a straightforward way to fill a lexical gap. The borrowing of vocabulary items is called lexical diffusion. This reflects the fact that the entire vocabulary of a language constitutes a lexicon, with individual vocabulary items or words constituting being lexical item. In addition to lexical diffusion, other features can diffuse as well, for example diffusion of phonological, morphological, syntactic, syntactic, or event pragmatic features is possible. Lexical diffusion: borrowing of vocabulary items The most common way that languages influence each other is the exchange of words. Much is made about the contemporary borrowing of English words into other languages, but this phenomenon is not new, and it is not very large by historical standards. The large-scale importation of words from Latin, French and other languages into English in the 16th and the 17th centuries was more significant. Some languages have borrowed so much that they have become scarcely recognisable. Armenian borrowed so many words from Iranian languages, for example, that it was at first considered a divergent branch of the Indo-Iranian languages and was not recognised as an independent branch of the Indo-European languages for many decades. Diffusion of other language features The influence can go deeper, extending to