An outside plant is all the hardware including cabling, repeaters, towers, poles, and cabinets located between demarcation points in switching facilities and the end user device.
The term "outside plant" (OSP) originated in the late 1800s. As Alexander Graham Bell's invention grew in popularity and the Bell System was formed, the new company needed to organize its operations into manageable areas of responsibility. These areas were defined as "plant departments." "Inside plant" (ISP) encompassed the switchboards that were later replaced by telephone switching machines we now call central offices. OSP referred to the facilities and all related components from the switchboard to the subscriber's telephone set.