Simply put, it is the amount of data that can be transferred through a digital connection in a given time period (i.e., the connection's bit rate), usually measured in bits or bytes per second. Therefore the bandwidth of the Enterprise 2000 Account is 2048kbps.
Our less expensive broadband accounts have a limited amount of transfer usage or 'Bandwidth Allowance' - ie. the total amount of traffic (uploads and downloads) that take place on your line in a specific amount of time (eg. a month). For example, if you download an artwork file of 17mb and send 2 emails each with a picture attachment of 1.2mb, your total bandwidth usage for that session will be 19.4mb.
Try the Bandwidth Calculator to see how much you might use in a month
Don't panic! There is a small charge per Gb that you go over your Bandwidth Allowance in a month - please see the Broadband Order Form for pricing. There is a free utility recommended by ADSLguide.org.uk that can be used to measure bandwidth on individual computers called NetMeter - download here - so you can keep an eye on your bandwidth usage.