What is a Control in a Science Experiment?

A control in a science experiment is a group of subjects or objects that are not exposed to the variable. Say you are wondering if green beans can grow in the dark. Your control group would be the group that is not put in the dark. You have to have a control to see if the variable works. In drug trials the control group is given a placebo. It helps you tell what is normal in an expirement and if your experiment is working.