"Dioxins" refers to a group of chlorinated organic chemicals with similar chemical structures. In all GreenFacts publications the term "dioxins" is used to cover both polychlorinated dibenzo-dioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs). Other sources may refer to these compounds as "dioxins and furans". Some dioxins have harmful properties, depending on the number and position of chlorine atoms. One of the most toxic dioxin is known as TCDD (2,3,7,8 tetrachlorodibenzo-p-dioxin). Some PCBs which have similar properties are considered "dioxin-like".