To understand what lies behind the whole internet means a journey back in time to the invention of the telephone. By laying wires from house to house, from house to exchange and from exchange to exchange, people could talk to each other over essentially two wires - one for send, another for receive.
When people wanted to send data over the same wires, a technology was invented where tones were sent and received to indicate certain characters and codes. To this day, the way that information is carried is based on the same encoding - the character 'A' has a code of 65, or in binary, 01000001 - and this code sent across in tones would be something like "low beep","high beep","low beep","low beep","low beep","low beep","low beep","high beep".
But the problem with transmitting the beeps was that the amount of bandwidth - the speed at which you could use the beeps, was limited by the telephone equipment. This bandwidth (the lowest sound to the highest sound) on the telephone was limited from 0 Hz to about 4000 Hz, or 4000 cycles per second. The highest note on a piano is 4186 Hz, so anything above this was lost. The range from 0 to 4000 is the "narrow" band.
Eventually it was realised that by encoding information at higher frequencies, and by using special equipment, it was possible to send more information. And by subtely encoding the 'tones' using complex methods called modulation, the speed of transmission could be vastly increased. Better yet, because the existing telephone equipment did not hear or need the higher frequency information, it was possible to hold a telephone call at the same time as being connected through a high speed data connection. And the band that contains the data is far wider than the narrow band used for regular telephone calls - a "broad" band.
This broad band carries much of the data (words and pictures, sound and video) on the internet today.
ADSL the abbreviation is Asymmetric Digital Subscriber Line. It is asymmetric because most users wish to receive more information than send it, so the download speed is typically much faster than the upload speed. You might download at four or eight times faster than the uploading speed.
Unfortunately, as the frequency gets higher, the distance that the signal will carry is much reduced. So for ADSL, the closer you are to the telephone exchange, the faster the signal can go. In the UK, broadband offers can be seen by checking out the 'distance to exchange' facility on the UK Broadband Availability Checker page (together with a Google Map) for any postcode or telephone number in the UK. It tells you the likely speed that you will be able to obtain from an Internet Service Provider and the kind of connection you might get (either a variant of ADSL or by using a cable company connection).
Some companies do not use the regular exchange facilities and manage the line connection themselves - this is called "Local Loop Unbundling" and can lead to even faster equipment being provided. More and more lines are being unbundled and this provides even more choice for the consumer.
Broadband is a revolutionary technology and makes the world a very small place - and provides online shopping, banking, entertainment and research information. Competition means that pricing is very keen and there are many companies seeking to win business.