Assimetric Digital Subscriber Line
Digital phone line from the xDSL family.
This tecnology is called assimetric because it allows download speed to be different from upload speed.
It is implement through a pair of copper wires and its download speed can be up to 8 Mbps and its download speed can be between 16 Kbps and 640 Kbps. The maximum achieved speed depends on the line quality, on the cable quality and the distance between the computer and the phone station.
Actually these speeds are maxium theoretical. Phone companies can offer plans with lower speed grades (like 256 Kbps, 512 Kbps, etc).
ADSL lines have three channels: two data channels and one voice channel. This separated voice channel prevents your connection speed to be downgraded if you are using both data channels, what doesn't happen with ISDN. It also allows you to talk on the phone and surf the net at the same time.