Digital loop carriers (DLCs) consolidate the voice traffic of remotely located customers onto a few transport lines running back to the central office (CO), thus reducing the cost and space requirements of serving those customers. Asymmetric digital subscriber line (ADSL) technology is used to transport large amounts of data traffic over existing copper telephone lines—up to 8 Mbps downstream and 640 kbps upstream—while simultaneously supporting plain old telephone service (POTS). Complete Article

In Plain English:

DSL is a way to use your existing phone lines so it can carry more data and because it can carry more data ... its faster