A technology developed by Bell Labs to transmit compressed digital video and audio over regular (twisted pair) telephone lines with the use of special modems. It entails one high-speed, unidirectional data channel and one low-speed, bidirectional control channel (making it asynchronous). Basically, this means you can download faster than you can upload.
Like DSL, this technology uses the existing copper wiring found in almost every home and office to provide a faster connection to the Internet. Special hardware is attached to both ends of the line to allow data to transmit over the wires at a far greater speed than the standard phone wiring (POTS). ADSL supports data rates from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).