Synonymous with off-premises station (OPS). A key telephone system (KTS) or PBX station or extension that terminates on a telephone physically located off-premises, typically on a non-contiguous property. In addition to a special line card, an OPX requires a dedicated private line, typically leased from the local exchange carrier (LEC).The OPX enjoys all of the features of an extension located on-premises, but at considerable cost. OPXs are, and always were, uncommon, but sometimes are used to connect a distant guard shack or security building to the PBX or perhaps to provide a technically challenged key executive with a PBX extension at home. See also KTS, LEC, and PBX.