A placebo is an inactive substance or treatment that is given to a person in place of a drug or other active treatment. Placebos are often used in clinical trials as a control group to compare the effects of a new treatment to the effects of a placebo.
The placebo effect is a phenomenon where a person experiences an improvement in their symptoms or condition after receiving a placebo. This is believed to be due to the person's belief in the effectiveness of the treatment, rather than the actual chemical or physical effects of the placebo itself.