ADSL (Asymmetric Digital Subscriber Line) is a type of broadband internet connection that uses existing telephone lines to transmit data. It is called "asymmetric" because the download speed is typically faster than the upload speed. ADSL technology allows for internet access and telephone service to be used simultaneously on the same line without interference.

Here are some key features of ADSL:

1. Download vs. Upload Speed: Download speeds are faster than upload speeds, making it ideal for activities like browsing, streaming, and downloading files.

2. Connection Type: ADSL uses standard copper telephone lines, which are widely available, making it a common choice in areas where fiber-optic connections are not yet available.

3. Distance Limitation: The speed of ADSL decreases the further you are from the telephone exchange (central office), which can affect internet performance.

4. Simultaneous Use: You can use the internet and make phone calls at the same time because ADSL divides the line into separate frequency bands for data and voice transmission.

5. Modem Required: To use ADSL, you need a special ADSL modem to connect to the internet through the telephone line.

ADSL has largely been replaced by faster technologies like fiber-optic and VDSL, but it remains a viable option in some rural or remote areas.