The term "placebo group" refers to a control or comparison group in clinical research, where participants receive an inactive treatment or fake intervention that is designed to resemble the real treatment as closely as possible. The purpose of having a placebo group is to provide a basis for comparison and ensure that any observed effects of the tested treatment are genuine and not due to other factors such as expectations or spontaneous improvement. In this way, researchers can better understand whether the intervention being studied has an actual effect on participants' outcomes beyond what would be expected from natural changes or other influences.