A pharmaceutical is any kind of drug used for medicinal purposes, like cough syrup or sleeping pills.
You may have heard of a pharmacy, which is a place where you can buy medicinal drugs, or a pharmacist, which is a person who prepares those drugs. In general, a pharmaceutical is anything related to pharmacies or pharmacists, though it especially refers to the kinds of medicines that they sell. Pharmaceuticals are often contrasted with what are called recreational drugs, which are the illegal kind that are generally used for entertainment purposes rather than to help heal the body.
