Cookies are a very useful tool in maintaining variables on the Web.
Cookies can store database information, custom page settings, or just about anything that would make a site individual and customizable. For example, an airline site may set a cookie indicating a particular passenger prefers aisle seating. Cookies are small data structures delivered by a Web site to a user. The Web site may deliver one or more cookies to the client. The client stores cookie data in one or more files on its local hard drive.