The article discusses the terms used in learning a second language or a foreign language. It explains that acquiring a second language happens unconsciously, while learning a foreign language is a conscious process. Language aptitude is the natural ability to learn a language. Bilingualism can result from different language learning strategies. Interlanguage is a mix of native and learned language rules. Language competence is knowledge of a language, language performance is using language, and language proficiency is the ability to communicate effectively. These terms are being introduced into Ukrainian science.