The term 'HALOGEN' refers to a group of elements in the periodic table, including chlorine and fluorine. Chlorine and fluorine are both non-metallic elements that are highly reactive and form compounds with other elements. They are both used in a variety of industrial and commercial applications, such as water purification, bleaching, and refrigeration. Chlorine is also used in the production of plastics, while fluorine is used in the production of pharmaceuticals.