Abstract: This article explores such categories of conceptual framework of risk management as “disaster” and “disaster risk”. The closeness of these terms at times leads to an unreasonable substitution of one term for another, which is justified by the ambiguity of definitions used in the Russian literature, as well as regulatory documents and standards. Securing the reliable methodological foundations of risk management of socioeconomic systems, requires clear demarcation of the risks of disasters and disaster risks, providing their precise definitions. The term “disaster risk” describes the most hazardous category of risks by severity level of its consequences, regardless of the nature and means of realization. The author proposes an original definition of disaster risk as a risk, the realization of which leads to impossibility or unreasonableness of functionality of the system. Such definition is structured on the basis of qualitative criterion and is applicable for any socioeconomic systems. The concept of “disaster” does not have a rigorous scientific definition, and describes more of an emotional and psychological assessment of the case of damage, rather than its qualitative essence. The definition proposed by the World Health Organization, which in its revealed for may be interpreted as an “unfavorable occurrence with severe consequences”. At the same time, the definition of “disaster” may have a precise legal interpretation, based on the use of quantitative criteria. The author suggests an original constructs of such definition, which can be applied in regulatory documents, which requires an unequivocal classification of the event as “disaster” in terms of making legally significant solutions, for example, regarding allocation of funds for accident and disaster relief.