Halogen n. : An electro-negative element or radical, which, by combination with a metal, forms a haloid salt; especially, chlorine, bromine, and iodine; sometimes, also, fluorine and cyanogen. See Chlorine family, under Chlorine.

Example:
How do I replace a Halogen tube in a Halogen tube radiator heater?

Taxonomy
halogen, fluorine, compounds, bromine, iodine, elements, atoms, aq, bonds, chemical reactivity, aliphatic, halogen elements, Cl2, borders, halogen molecules, free encyclopedia, liquid, gases.

Defination from the web:
halogen. ... Some properties, however, are found in neither parent halogen. ... For aliphatic carbon-halogen bonds the C-F bond is the strongest and usually less chemically reactive than aliphatic C-H bonds. ...