What is the term that defines the end of the provider's responsibility and the beginning of the customer's responsibility?

The demarc, or demarcation point, is the end of the provider's responsibility for the connection and the point where the customer's responsibility begins. This point is often a physical location where the provider can test their connection and hand off the service to the customer. Customer premises equipment (CPE) is the router or ancillary equipment used to facilitate the connection to the wide area network (WAN). The central office (CO) is a physical location where all of the customer connections on the local loop meet up and WAN services are delivered. The CO is also sometimes referred to as the point of presence (POP).