Treatment Group

The group that receives the new thing you are testing — the new feature, the new drug, the redesigned page. In an A/B test it is usually called variant B or simply “treatment”.

The treatment group exists to answer “what happens when we make the change?”, but its number is meaningless on its own. A 5% sign-up rate in the treatment group only becomes informative when you compare it against the control group; maybe sign-ups are 5% every week regardless of your change.