The cookie may be a Drupal or PHP session cookie. Drupal is as PHP application. PHPSESSID is the default PHP session cookie name. Drupal overrides this default with a name starting with SESS, followed by a hash. The hash is a hexadecimal representation of an MD5 hash of the session name or the value of the cookie_domain setting in the settings.php file. Since you blocked the name, I can't tell for sure whether taht is what you are seeing. This may help.