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Meaning of bandwidth in web hosting
In website hosting, the term "bandwidth" is often used metaphorically, to describe the amount of data that can be transferred to or from the website or server, measured in bytes transferred over a prescribed period of time. This can be more accurately described as "Monthly Data Transfer."
Web hosting companies often quote a monthly bandwidth limit for a website, for example 500 gigabytes per month. If visitors to the website download a total greater than 500 gigabytes in one month, the bandwidth limit will have been exceeded.
From : http://en.wikipedia.org/wiki/Bandwidth