From Overview of Advanced JavaScript -- Web Scripting Language CPS616 Technologies of the Information Age -- Spring Semester 98. byTom Scavo,Geoffrey C. Fox
A cookie is:
a named string stored by the browser
a property of the Document object
The cookie mechanism gives the browser a kind of memory, that is, a cookie "saves state"
Originally, only CGI scripts could read/write cookie strings, but with JavaScript, cookies are handled entirely on the client side