2. Definition and explanation

Bandwidth measures of the capacity of a communications channel.

Digital Bandwidth is the maximum amount of data that can travel along a communications channel in a given time.

The smallest piece of digital data is the 'bit' and time interval is measured in seconds

And so a sensible measure of data capacity is "bits per second".

However, a channel having a capacity of only a few bits per second is extremely slow!

But think "Lighthouse".

You are out at sea on a stormy night and you see a lighthouse signal - it flashes ON and then it is OFF for a while. This is digital data - the lighthouse signal takes a second or so to flash, so in this case the bandwidth would be about 1 bit per second and it is a life saver to stop your boat hitting those rocks.

But apart from a flashing lighthouse, a 1 bit per second link is not that useful.

Courtesy of Wikimedia Commons