ADSL stands for: Asymmetric Digital Subscriber Line
ADSL broadband is a connection provided over home telephone lines. Openreach owns the UK's landline infrastructure, so when you have an ADSL connection, you need to rent your phone line from Openreach. If you already have an existing phone line, the broadband is added onto the package.
How does ADSL broadband work?
ADSL is the name given to a broadband connection which works through the copper wires of your existing phone line. Because it comes through the Openreach phone line network — which most homes are already connected to — it's the most popular type of broadband available, simply because it's so easy to sign up to and requires minimal installation in most cases.