Generally speaking, there are mainly three kinds of variables involved in scientific experiments: independent variables, dependent variables and control variables  Independent variables are variables that are manipulated by the experimenter in an experiment  A dependent variable is a variable that changes as the independent variable changes
Control variables refer to potential factors or conditions other than independent variables in an experiment that affect experimental changes and results
Studying that the supply of wheat is affected by the local purchase price, the supply of wheat is the control variable, and the purchase price is the dependent variable