What is placebo?
placebo is Any dummy medical treatment or intervention. Originally, a medicinal preparation having no specific pharmacological activity against the person’s illness or complaint and given solely for the psychophysiological effects of the treatment. More recently, a dummy treatment administered to the control group in a controlled clinical trial in order that the specific and non-specific effects of the experimental treatment can be distinguished.
source: A GLOSSARY OF TERMS FOR COMMUNITY HEALTH CARE AND SERVICES FOR OLDER PERSONS. World Health Organization, 2004.