DSL (Digital Subscriber Line) is a broadband technology that comes in many different flavours and often uses an existing PSTN/POTS telephone line to communicate. It's not unlike a dialup modem, yet moves data far faster and can even split the voice and data elements of a single phone line into two separate parts (not all country's can do this, although BT in the UK does).

Types of DSL include ADSL , ADSL2 , ADSL2+ , SDSL , VDSL , VDSL2 , VHDSL etc.

Full Details:

http://www.ispreview.co.uk/broadband_DSL.php