- Asymmetric Digital Subscriber Line.
ADSL is a technology to transmit digital information at high bandwidths across existing copper phone lines. Download speeds are typically much faster than upload speeds (hence the term "asymmetric").
Also more commonly referred to simply as "broadband" - although broadband can be provided using technologies other than ADSL (such as cable).
For more information see:
- http://everything.explained.at/Asymmetric_Digital_Subscriber_Line - ADSL Explained.