The physical wiring that connects a subscriber to the public switched telephone network (PSTN). A subscriber's phone is connected to the inside wiring which is connected to a Network Interface Device (NID) which patches the inside wiring to the outside wiring of the local loop.
Since this connection is local to the subscriber, it is called the local loop. Because this local connection spans the last few miles to the customer's location, it is also frequently called the last mile. In modern phone systems, the local loop runs from the last digital data point to the subscriber's premise and back.