A cookie is a small piece of information that you ask a browser
to remember for you. This is handy, since many people ma be
visiting your site. For instance, you may want to "remember" a
person's name, or some preference.
Later on, you can examine any cookies that you may have set, these will be in the PHP array $_COOKIE. ( see an example page)
By default, cookies expire (the browser removes them) when the
browser is closed. If you set a time to expire, in the 3rd
argument, the cookie will be kept until that time.
To "expire" a cookie, set a past time, such as time()-1.
setcookie ("dog"); // cookie set, without a value
setcookie ("cat", $_GET['catsname']); // cookie set, with value from a form
setcookie ("horse","Seabiscit", time()+60*60*24*30); // expires in 30 days
print "The old cat name was: " . $_COOKIE['cat'];
// previously set cookies will be in the COOKIE array
A third party cookie is a cookie set, not by a page you browse to, but by a banner ad that is included in some page you visit. These are used by advertisers to build a profile of consumer preferences. You should consider setting your browser to not accept third party cookies.