A parameter, also known as a parametric variable, is a variable. When we study the current problems, we are concerned about the changes of some variables and their relationships. One or several of them are called independent variables, and the other or several are called dependent variables. If we introduce one or some other variables to describe the changes of independent variables and dependent variables, then the introduced variables are not the variables that must be studied in the current problem, and we call such variables parametric variables or parameters.