A piece of information sent by a Web server to a user's browser. (A Web server is the computer that "hosts" a Web site, and responds to requests from a user's browser.) Cookies may include information such as login or registration identification, user preferences, online "shopping cart" information, etc. The browser saves the information, and sends it back to the Web server whenever the browser returns to the Web site. The Web server may use the cookie to customize the display it sends to the user, or it may keep track of the different pages within the site that the user accesses. Browsers may be configured to alert the user when a cookie is being sent, or to refuse to accept cookies. Some sites, however, cannot be accessed unless the browser accepts cookies. This definition is from:
http://www.getnetwise.org/glossary.php