A cookie is the term given to describe a type of message that is given to a Web browser by a Web server. The main purpose of a cookie is to identify users and possibly prepare customized Web pages or to save site login information for you.
When you enter a Web site using cookies, you may be asked to fill out a form providing personal information; like your name, e-mail address, and interests. This information is packaged into a cookie and sent to your Web browser, which then stores the information for later use. The next time you go to the same Web site, your browser will send the cookie to the Web server. The message is sent back to the server each time the browser requests a page from the server.
A Web server has no memory so the hosted Web site you are visiting transfers a cookie file of the browser on your computer’s hard disk so that the Website can remember who you are and your preferences. This message exchange allows the Web server to use this information to present you with customized Web pages. So, for example, instead of seeing just a generic welcome page you might see a welcome page with your name on it.