The amount of data that is passed between a web site and a user’s web site is measured in terms of bandwidth. For example, if your Web site has a bandwidth of 10GB a month and the site contains a 1MB picture - that picture can be viewed 10,000 times each month. At that point you will have reached your bandwidth allotment. You will then have to purchase additional bandwidth if you wish to have more visitors to your site.
In most instances bandwidth is purchased on a per month basis and is reset each month. If you expect that your web site will generate a lot of traffic you should consider a hosting plan that has an ample amount of bandwidth. If you just have a basic site that is for family or friends, you may not need a large bandwidth. If you are unsure about the amount of bandwidth you will need, you might want to select an average plan and then upgrade or even downgrade your plan if you need to change your bandwidth allotment.