Every hosting account comes with a set allocation of data-transfer (or bandwidth as it is somethimes called). This is effectively the 'traffic' that your account uses.
It is the amount of files and data that you can transfer per month. The standard allowance you get is 6000MB of bandwidth per month. Everytime a visitor views your site they are downloading files from your site, this uses your bandwidth. If you have a page that is 30kb in size including images and 10 people view that page you would have used 300kilobytes of bandwidth.(1000MB = approximately 1,000,000 kilobytes).
Generally if you make available large files for download - (video or audio) then you will use 'more bandwidth'. However - it's worth noting that less than 1% of our customers user over the set allocation.
It is often possible to lower your bandwidth usage by perhaps removing large files and/or popular areas of your website.
You can upgrade your bandwidth allowance at any time. Please contact support should you wish to do this.