In order to be able to determine where certain links are coming from, a code is often inserted into the URL (uniform resource locator).
For example:-www.somethingsomethingsomething.com/blahblah.php?SOMELONGCODE
These codes are used primarily in paid search campaigns or in affiliate marketing. In affiliate marketing the code usually contains two parts. One will identify the affiliate the second will usually identify his campaign (for internal tracking – for example an affiliate that uses a different code in e-mail and web traffic campaigns). These will allow the affiliate to get paid but also to track which link source is working out the most profitable for the business. For paid search campaigns a lot more information is provided including the keywords that were searched. The end result is the same, the user can examine statistics about which keywords were most profitable, which way of wording an advertisement delivered the most clicks etc.