What is bandwidth?
Bandwidth is the amount of information you are allowed to send through a servers internet connection. If you have a file that is 2 MB and it is viewed or downloaded 100 times in a month, then you will have used up 200 MB of bandwidth.
There are many web hosting services that offer "Unlimited Bandwidth". This is nice in that you will never get any extra overage fees do to excess traffic. Even hosting plans that offer "only" 300 GB of data transfer are far more than enough for most sites, with rare exception. Only the web sites that receive extremely large amounts of traffic viewing large multi-media video files will ever likely exceed this limit.