On the World Wide Web, a block of data that a Web server stores on a client system. When a user returns to the same Web site, the browser sends a copy of the cookie back to the server. Cookies are used to identify users, to instruct the server to send a customized version of the requested Web page, to submit account information for the user, and for other administrative purposes.
— Computer Sciencea piece of information sent by a Web- Server- to a Web- Browser- that the Browser software is expected to save and to send back to the Server whenever the browser makes additional requests from the Server.
— Computer Science