A cookie is a text-based data file which a website can require to save information on the computer of the website visitor. Cookies are often used to enable access to different functions or services on the website.
The information contained in cookies varies from website to website but usually concerns information which enhances the user experience.
The cookie used at the Challenges Forum website is used to gather information about how the pages on the website are used. Information about which server your computer is connected to, what kind of browser you are using, how often you visit the website etc is stored collectively.
The information is used in the purpose of producing statistics about the frequency of usage of the website.