There are many terms which refer to Polish language and they do not have the same meaning. The differences however, even minor, are particularly important in the area of language learning and teaching for both researchers and instructors (teachers of Polish as a mother tongue and as a foreign language). Not only should they be able to differentiate between various terminological categories but also be aware of their theoretical and practical implications, e.g. what is the function of Polish when it is not the pupils’ first language? what role does it play for its speakers? what is the difference between language learning and language acquisition, between bilingualism and knowledge of two languages? what is semilingualism and diglossia? These issues are closely linked with multilingualism and multiculturalism which in today’s society have become phenomena characteristic of many communities.