What does it mean to have a control group

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

Control group is a group in a lab or project that is completely controlled and you know exactly how you want it to go. Example: you have your controlled group of cereal and theyre all froot loops with the same cereal same bowl. the opposite of that would be having the same bowl, same milk, and 3 different cereal brands.