Your monthly data transfer/bandwidth allowance is the total amount of data travelling to and from your website within a one month period.
Everytime someone views your website they download data from your webspace. Similarly, everytime you make an adjustment to your website (e.g. adding a new page or image) you are uploading data to your webspace. The more uploading and downloading that occurs from and to your webspace the more bandwidth/data transfer allowance you will use.
The amounts shown are measured in Gigabytes (GB). If you should go over your allowance limit you will be subject to our over-usage charges - dont worry though, these are very reasonable prices and our automated systems will warn you if you hit your limit (please contact our support team to find out the current rates for bandwidth over-usage).