The term is an acronym for Private Branch eXchange. A PBX, sometimes known as a telephone switch or phone switching device, is a system that connects office telephone extensions with the public network.

A polymer-bonded explosive, also called PBX or plastic-bonded explosive, is an explosive material in which explosive powder is bound together in a matrix using small quantities (typically 5–10% by weight) of a synthetic polymer ("plastic"). Note that despite the word "plastic", polymer-bonded explosives are not hand malleable after curing, and hence are not a form of plastic explosive.

PBXs are normally used for explosive materials which are not easily meltable to cast or which are otherwise hard to form.