Wiktionary
a. (context inorganic chemistry English) Involving a bond between two halogens, or a compound formed by such a bond. n. (context inorganic chemistry English) Any binary compound of two different halogens; an interhalogen compound
Wikipedia
An interhalogen compound is a molecule which contains two or more different halogen atoms ( fluorine, chlorine, bromine, iodine, or astatine) and no atoms of elements from any other group.
Most interhalogen compounds known are binary (composed of only two distinct elements). Their formulae are generally XY, where n = 1, 3, 5 or 7, and X is the less electronegative of the two halogens. They are all prone to hydrolysis, and ionise to give rise to polyhalogen ions.
No interhalogen compounds containing three or more different halogens are definitely known, although a few books claim that and have been obtained, and theoretical studies seem to indicate that some compounds in the series are barely stable.