A "treatment group" refers to a specific group of people who receive a particular type of treatment or intervention in a study or experiment. Full definition
Families in treatment group 1 (n = 94) were provided sensory and developmental screening for the child at 12 and 24 months of age. (jamanetwork.com)
We did find an indication, however, that the recruitment source might predict course of depressive symptoms independent of treatment group assignment. (bmjopen.bmj.com)
Additionally, patients in the active treatment group showed a higher level of weight loss (over 5 kg) whilst receiving medication. (sciencedaily.com)