Dioxin is any of a family of compounds known chemically as dibenzo-p-Dioxins.

Concern about them arises from their potential toxicity as contaminants in commercial products. Tests on laboratory animals indicate that it is one of the more toxic anthropogenic (man-made) compounds.

Other definition:
A dioxin is a man-made chemical By-product formed during the manufacturing of other chemicals and during incineration. Studies show that dioxin is the most potent animal Carcinogen ever tested, as well as the cause of severe weight loss, liver problems, kidney problems, birth defects, and death.