The libraries polycultural activities are connected with their work in the polycultural environment. The article deals with the terminology used by libraries for this activities, defines these terms. It reveals reasons for the multicultural librarianship appearance in Europe and creation of IFLA Section «Library services to multicultural populations». The author shows definitions of «multiculturalism» and «multicultural library services» given by the International Guidelines «Library services to multicultural communities»; the difference between the conditions of creation and development of multicultural library services in Europe and the Russian libraries work in the polycultural environment. The paper represents a comparative analysis of such definitions as «multicultural» and «polycultural» by the academic Russian environment and English dictionaries. The author concludes that in our country it would be more correct to use the term «polycultural», which involves the interaction of cultures, unlike the term multicultural meaning the existence of several cultures in a society. That’s why the author speaks about the polycultural activities of Russain libraries, or about their activities in the polycultural environment aimed at interaction and mutual influence of cultures.