The purpose of this paper is to explain the connotation of grey number, which is the basic unit of grey mathematics and the key to establish the mathematic framework of grey system theory.
From the grey hazy set, the paper re‐defines grey number and the operation of grey‐number element, then some properties are obtained. Based on them, the operation of grey‐matrix element is given. The general definition of grey function and its operation are also proposed.
The connotation of grey number is elaborated and the elementary framework of grey mathematics can be established.
The researched object, objective and techniques of grey system theory have not been logically proposed and they may influence the comprehension of grey system theory. The obtained results of grey mathematics may significantly promote its development.
The paper can enable managers to control the complex system with missing information by using the quantitative approaches.
Grey mathematics may become a branch of mathematics to deal with proximate calculation.
