A cookie is a small data file that is placed on the hard drive of your computer when you visit a web site. A "session cookie" expires immediately when you end your session (i.e., close your browser). A "persistent cookie" stores information on the hard drive so when you end your session and return to the same web site at a later date the cookie information is still available.
If you would like to opt out of accepting cookies altogether, you can generally set your browser to not accept cookies or to notify you when you are sent a cookie, giving you the chance to decide whether or not to accept it. However, certain features of our web sites or other services may not work if you delete or disable cookies.