On the understanding of risk concept

Risk is everywhere, and people have to cope with risks. In order to establish a scientific theory of risk, three core problems should to be solved, there are how to define risk, how to express risk in a proper mathematical form and how to measure risk. On the basis of common understanding of domestic and foreign scholars on risk definition, a complete risk definition is presented based on the uncertain information. Five basic attributes of risk are given, including harmfulness, possibilities, dynamic, subjection and complementarity. Then it has a detailed description of each attribute, especially harmfulness that is considered to be the essential attribute.