This refers to how much data transfer your web host allots to run through your website. If, for example, the file size of your home page is 50 KB then every time someone visits or 'hits' your home page this counts as 50 KB worth of data being transferred from your website and hence you will have used up 50 KB worth of 'bandwidth'.

If you get 20 hits on your home page then will have used up 1MB worth of bandwidth. If you get 2000 hits on your home page then you will have used 100 MB worth of bandwidth. If you have 10 pages all with a file size of 50 KB and they get 2000 hits each then you will used up 1 GB worth of bandwidth. Etcetera. The number of hits your website gets in a specified period of time is colloquially referred to as 'traffic'. So if you have a website getting 1 million hits a day then you are getting ALOT of traffic.

Bandwidth limitations are usually specified in terms of how many megabytes (MB) or gigabytes (GB) per month and can vary anywhere from 300 MB (find another web host) to 2000 GB (good) and upward per month. When you go over your allotted bandwidth you will usually be charged extra and the overage charges can sometimes be exhorbitant so it's good to get out the calculator and do the math on what kind of bandwidth you expect to use. This is just basically average page size X number of pages X average number of hits per page. If you have no idea what this will be then you're going to have to take your chances and sign up with a web host that has a good web stats program so that you can closely monitor the traffic to your site for the first little while to get a sense of what's going on.

Once you have approximated how much bandwidth you expect to use (or are actually using) then tack on a big chunk of extra bandwidth to your estimate to act as a kind of buffer zone allowing for extra good days or sudden increases in traffic. You'd be surprised at what a few inbound links from a high traffic website can do to your bandwidth. If you have a good website that is bound to attract alot of visitors or entice others to link to your website (which is the whole point) then it's best to BE PREPARED. 1 to 5 GB bandwidth is reasonable for new websites that are not Flash presentation or software download sites.