What is ADSL?

ADSL stands for Asymmetrical Digital Subscriber Line. Broken down into individual components, the phrase means:

Asymmetrical: Different speeds for transmitting and receiving data.

Digital: Signals representing data in patterns of 1 and 0

Subscriber Line: A connection between your premises and your local BT telephone exchange (DLE)

Since the service is digital, it can attain much higher speeds than a dial-up modem and experience far less errors. The wavelength at which it is transmitted is much smaller, the signal can be sent down the same piece of wire that is also used for voice/fax calls. Additionally, because the data is transmitted using TCP/IP, it can be verified upon receipt and re-sent if it arrives damaged. This allows for "error free" transmission.