This cookie is used to establish and continue a user session with your site.
When a user views a page on your site, the Google Analytics code attempts to
update this cookie. If it does not find the cookie, a new one is written and
a new session is established. Each time a user visits a different page on your
site, this cookie is updated to expire in 30 minutes, thus continuing a single
session for as long as user activity continues within 30-minute intervals. This
cookie expires when a user pauses on a page on your site for longer than 30 minutes.
You can modify the default length of a user session with the _setSessionCookieTimeout() method.