In his several recent articles, Yury N. Stolyarov has formulated strategic tasks for the library science, in particular, to update urgently the definition of “the library” in official documents with the focus on library activities as a social good. In this connection, the author argues that theoretical knowledge has to be developed in librarianship to develop essentially unambiguous terminology. The system approach proves to be efficient for formulating key concepts in the library science. This approach eliminates mistakes when determining the integrity of elements making the system essence of the object under study. “The library” is a key c oncept o f t he l ibrary s cience; t hough i t h as b een a mbiguous f or t he l ong time with the extension and content changing according to historical ideas of this phenomenon. The abstract ideas of the library have been developing in a quite traditional way, i. e. from static (points, lines, planar geometric figures, 3-dimensional objects) to dynamic ones. The author supports the proposal to formulate different definitions of the library, i. e. for the professional and national standards, which would enable to describe the reality with the greater precision. Based on her theoretical studies, the author suggests updated definitions of: “the library” scientific category, the concepts of “the library as a social institution”, “personal library” and “the library as an organization; as only “the library as a social institution” is subject to regulation by normative documents. Differentiation of “the library” scientific concept into specific ones makes the foundation for formulating different definitions for the professionals and national standards.