In HTTP, a cookie is a piece of information sent to the web browser for the browser to send back to the web server on subsequent requests. Cookies are most commonly used to identify of a particular user across multiple accesses, but they can also be used to store preferences and other persistent-state information without specifically tracking a given user.
In PHP, the $_COOKIE built-in global array and setcookie() function are the most common means of retrieving and setting cookies, but PHP does have an extensive selection of cookie-management functionality.
Apparently the distinction between a cookie named "vbzcart.key" and another named "vbzcart_key" is ambiguous. I was having trouble using the former (it never seemed to be retrievable), so I changed the name to the latter -- and then found that I had two cookies. Retrieving the value of "vbzcart_key" gave me the value "vbzcart.key" (as indicated by the cookie list in Firefox 3). Deleting the "vbzcart.key" cookie from Firefox solved the problem. --Woozle 15:53, 26 July 2009 (UTC)