HTTP cookie
<World-Wide Web> A packet of information sent by an
HTTP server to a
World-Wide Web browser and then sent back by the browser each time it accesses that server.
Cookies can contain any arbitrary information the server chooses and are used to maintain
state between otherwise stateless
HTTP transactions.
Typically this is used to authenticate or identify a registered user of a
web site without requiring them to sign in again every time they access that site.
Other uses are, e.g. maintaining a "shopping basket" of goods you have selected to purchase during a session at a site, site personalisation (presenting different pages to different users), tracking a particular user's access to a site.
(http://www.illuminatus.com/cookie).
