The term "treatment group" refers to a specific category or subset of individuals within an experiment, study, or clinical trial who are being given a particular intervention, treatment, medication, or therapy that is being tested for its effectiveness. In other words, it's the group of people receiving active treatment in contrast to a control group which receives no treatment or placebo. The results obtained from this group help researchers determine whether the treatment has any positive impact on the condition they are studying and if so, how effective it is compared to not receiving the intervention at all.