A halogen is a type of gas that's used for lighting and other things.
When people talk about halogens, they often mention them in relation to light bulbs. Halogen bulbs are very common in many homes because they use less energy than some other types of bulbs while still producing bright light. The reason you might notice them is because they can get very hot - sometimes too hot to touch! Some cars even use halogen headlights, which help drivers see the road at night.
(chemistry) Any element of group 17, i.e. fluorine, chlorine, bromine, iodine, astatine and tennessine.
