Dioxins is the name for a group of chemical compounds. These are organic compounds. Polychlorinated dibenzodioxins (PCDDs), or simply dioxins, are a group of halogenated organic compounds which are significant because they act as environmental pollutants. They are very poisonous. Many dioxins cause cancer. Today, Dioxins are no longer made. They can occur as a by-product of other processes, though. Examples where dioxins can result are the production of PVC or the bleaching of paper. In nature, they are produced in volcanoes and forest fires.
A chemical accident where a lot of dioxin was released was the Seveso disaster.