DSL (Digital Subscriber Line) is a broadband technology that comes in many different flavours and often uses an existing PSTN/POTS or twisted pair copper 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.
Common types of DSL include ADSL , ADSL2 , ADSL2+ , SDSL , VDSL , VDSL2 , VHDSL etc.
Full Details:
http://www.ispreview.co.uk/broadband_DSL.php
Related Articles:
> POTS - Plain Old Telephone Service
> PSTN - Public Switched Telephone Network