The elements of group-17 in periodic table F, Cl, Br, I and At, these five elements together are called halogen. The meaning of the word halogen is salt matter.
They form halide ion by receiving one electron at their outermost energy level. The main source of halogen is sea salt. They are all non-metals. They react with metals to form salts and so, they are called halogens.
For example, 2Na (Metal) + Cl2 (Halogen)—-> 2NaCl (Salt)