a workplace that serves as a telecommunications facility where lines from telephones can be connected together to permit communication

A switching center for interconnecting the lines that terminate herein. It is also known as the Central Office or CO.

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls. A central office is the physical building used to house inside plant equipment including telephone switches, which make phone calls "work" in the sense of making connections and relaying the speech information.