What is a control group in an experiment

A control group is a group in an experiment or study that does not receive treatment from the researchers and is then used as a benchmark to measure how the other tested subjects do.

The control group is the object that is untouched to see the difference. For example, you are trying to find what compost is better for plants. You have 3 plants and 2 different types of compost. you put one type in each plant except for one. The one without compost is called the control group.