A multilingual person is someone who can communicate in more than one language, either actively (through speaking, writing, or signing) or passively (through listening, reading, or perceiving). More specifically, the terms 'bilingual' and 'trilingual' are used to describe comparable situations in which two or three languages are involved. A multilingual person is generally referred to as a 'polyglot', which may also be used to refer to people who learn multiple languages as a hobby.

Multilingual speakers have acquired and maintained at least one language during childhood, the so-called first language (L1). The first language (sometimes also referred to as the mother tongue) is acquired without formal education, by mechanisms heavily disputed. Children acquiring two languages in this way are called simultaneous bilinguals. Even in the case of simultaneous bilinguals, one language usually dominates over the other.

In linguistics, first language acquisition is closely related to the concept of a "native speaker". According to a view widely held by linguists, a native speaker of a given language has in some respects a level of skill which a second (or subsequent) language learner cannot easily accomplish. Consequently, descriptive empirical studies of languages are usually carried out using only native speakers.

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