What is bandwidth usage or "Hosting Bandwidth"?
This refers to the total amount of information that has been served to your web site visitors each month. Every file on your Web Site has a specific size (e.g. 20K). Every time a visitor downloads that file, your bandwidth usage goes up by that amount.
The larger the file, the higher the bandwidth usage when it is downloaded. The more traffic to your site, the more bandwidth you will use.