Originally Posted by REW Reed

The question mark starts the variable declarations in the URI. Another piece of syntax is the use of '&' to separate different declarations. This allows the page being viewed to change content and settings based on what the link contains. A good example is how you can link to a specific map in Google Maps:

http://maps.google.com/?ie=UTF8&z=4&om=1

If you click on this link, the page knows that you want the variable ie to be 'UTF8', z to be 2 and om to be equal to 1.

It is worth noting that this differs from internal data passing (post). Passing variables in the URI is often called a 'get' and is used for determining the state of the page (settings and such), whereas the 'post' method is often used when you want to enact a change, like to a database. This is why when you refresh a page you might see the pop-up confirmation 'This page uses POSTDATA. By refreshing this page you are resubmitting it'. The browser doesn't necessarily want you to delete your last blog twice or something more dire.

I hope this clears things up.