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. This kind of bilingualism is most likely to occur when a child is raised by bilingual parents in a predominantly monolingual environment. It can also occur when the parents are monolingual but have raised their child or children in two different countries.