Bandwidth (Data Transfer)
In general, any outward bound traffic from a web site, with the exception of e-mail, is considered to be data transfer.  Each time a web page, image, midi file, QuickTime video, etc. is sent to a computer accessing the site, the sizes of the files are tabulated.  Therefore, the actual amount of traffic depends on the content of the web page.  Text uses small amounts of bandwidth whereas pictures and graphics use much more.  Most sites use less than 1 GB (gigabyte) of traffic per month.  On average, that is equivalent to about 25,000 pages viewed.  Servers keep track of the content size to determine if usage is within the boundaries allowed for that type of account.