A control variable is an experimental element that is kept constant and unchanged throughout the course of an investigation. It is not of primary interest to the experimenter, but it is important to control it because it could influence the outcomes of the experiment. Control variables can be anything that is held constant or limited in a research study, and they can be controlled directly by holding them constant throughout a study or indirectly through methods like randomization or statistical control.

Control variables are important because they help prevent research biases like omitted variable bias from affecting the results. Any unexpected change in a control variable during an experiment would invalidate the correlation of dependent variables to the independent variable, thus skewing the results and invalidating the working hypothesis.

In summary, a control variable is an element that is kept constant throughout an experiment in order to assess the relationship between multiple variables. It is not part of an experiment, and it is not an independent or dependent variable. However, it is important to control it because it can affect the experiments result.