As a scientific term "risk'' originally appeared in insurance mathematics and meant the "ruin probability'' in a "collective risk'' model of an insurance company. Recently, this term has become widespread in different spheres of human activity and has been applied to various models of "individual risk". At the same time, despite its increasing popularity, its strict definition still does not exist, and various sources interpret it differently. The report discusses various interpretations of this notion and it reasons. The authors adhere to the concept of risk as a random phenomenon and from this point of view, consider its characteristics and their measuring methods. The risk tree is used for the probabilistic space of the risk phenomenon construction. In the talk, the proposed approach will be demonstrated with the help of one real-world example.