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1.
PBX
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.
Our company uses an IP PBX as a communication server.
by Rito Salomone, www.telecost.com October 05, 2006
 
2.
PBX
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.
JACK: So, we plant some PBX, jump ship, then blow it.

THOR: What is PBX?

TEAL'C: An explosive.
by Hans Olo May 05, 2009