File or part of a file put on a Web user's hard disk by a Web site .
Cookies are used to store registration data, to make it possible to customize information for visitors to a Web site, to target Web advertising, and to keep track of the products a user wishes to order online. Early browsers often enabled cookies to track which Web sites a user has visited and to retrieve data from other parts of the user's hard disk; current browsers prevent this and permit a site to have access only to cookies written by that site.