在不同的领域中，控制变量有以下不同的含义

在实验中，控制变量（或控制变因）是指在实验中需维持固定，不变动的条件。

实验中的控制变量一般都是会影响实验结果的条件，因此实验中需维持固定，以测试独立变量对实验造成的影响。例如一个有关波义耳定律的实验，确认气体体积和压力的关系，此时气体的温度即为控制变量。

The control variable (or scientific constant) in scientific experimentation is the experimental element which is constant and unchanged throughout the course of the investigation. The control variable strongly influences experimental results, and it is held constant during the experiment in order to test the relative relationship of the dependent and independent variables. The control variable itself is not of primary interest to the experimenter.