Bilingualism refers to the ability to speak and understand two languages. There are different types of bilingualism, including sign languages combined with spoken languages, or the ability to read a language without speaking it. Being bilingual means having ability in two languages within the same modality (such as two spoken languages) or across different modalities (such as a sign language and spoken language). While the definition of bilingualism is debated, it generally requires more than just reading or writing in another language. Child bilingualism is believed to provide benefits such as enabling communication across cultures, but some argue it could retard development of the native language or cognitive skills.