What is a URL parameter? Quite simply it is a string of characters, or a query string, that is appended to a URL that contains data. This data is passed to predefined web applications to find the appropriate content and return it back to the user’s web browser which then generates the entire web page. The query string can also be used for various other methods such as identifying a user’s session or using it as a way to look up information about your online bank account after you have logged in. URLs with parameters are used by various types of web sites however online shopping, auction, and banking type sites are probably the most prevalent.