The main purpose of this article is to systematize, to specify and to structure the realm knowledge management (KM). Historically, KM originates from such disciplines as knowledge engineering, psychology, management, computer science, and the main approaches are generated by different national cultures. As a result, we can observe the lack of clear definitions of used concepts and internal inconsistency of the discipline, which in turn leads to communication difficulties both inside academy and managerial practice. The main research question sounds like "What are the main elements of knowledge management as a subject area, and how are these elements interrelated?". To answer this question, we applied the ontological engineering method and carried out a deep structural analysis of the knowledge management domain. We identified the basic concepts of KM, determined the number of abstraction levels, distributed the concepts by levels and determined the main relationships between them. The main result is the ontology of knowledge management, or structural specification, which includes a dictionary of the main domain concepts, and visualizes the basic logical connections between them. We conducted a thematic literature review to avoid contradictions and inaccuracies. The proposed ontology combines taxonomy, partonomy and genealogy of knowledge management. We believe that this paper can be useful both to the academic community and to the practitioners, since it structures existing knowledge in the KM domain and it offers clear definitions of used concepts and the relations between them. It can help to synthesise the company common business vocabulary and language without ambiguity.