Core PHP: $_COOKIE (7.9)

Cookies

Cookies are often used to identify the user. A cookie is a small file that the server embeds on the user's computer. Each time the same computer requests a page through a browser, it will send the cookie, too. With PHP, you can both create and retrieve cookie values.

Create cookies using the setcookie() function:

setcookie(name, value, expire, path, domain, secure, httponly);

name: Specifies the cookie's name
value: Specifies the cookie's value
expire: Specifies (in seconds) when the cookie is to expire. The value: time()+86400*30, will set the cookie to expire in 30 days. If this parameter is omitted or set to 0, the cookie will expire at the end of the session (when the browser closes). Default is 0.
path: Specifies the server path of the cookie. If set to "/", the cookie will be available within the entire domain. If set to "/php/", the cookie will only be available within the php directory and all sub-directories of php. The default value is the current directory in which the cookie is being set.
domain: Specifies the cookie's domain name. To make the cookie available on all subdomains of example.com, set the domain to "example.com".
secure: Specifies whether or not the cookie should only be transmitted over a secure, HTTPS connection. TRUE indicates that the cookie will only be set if a secure connection exists. Default is FALSE.
httponly: If set to TRUE, the cookie will be accessible only through the HTTP protocol (the cookie will not be accessible to scripting languages). Using httponly helps reduce identity theft using XSS attacks. Default is FALSE.

The name parameter is the only one that's required. All of the other parameters are optional.