Cookie Type Duration Description
__utma persistent 2 years from set/update Used to distinguish users and sessions. The cookie is created when the javascript library executes and no existing __utma cookies exists. The cookie is updated every time data is sent to Google Analytics.
__utmb persistent 30 mins from set/update Used to determine new sessions/visits. The cookie is created when the javascript library executes and no existing __utmb cookies exists. The cookie is updated every time data is sent to Google Analytics.
__utmc session End of browser session Not used in ga.js. Set for interoperability with urchin.js. Historically, this cookie operated in conjunction with the__utmb cookie to determine whether the user was in a new session/visit.
__utmv persistent 2 years from set/update Used to store visitor-level custom variable data. This cookie is created when a developer uses the_setCustomVar method with a visitor level custom variable. This cookie was also used for the deprecated_setVar method. The cookie is updated every time data is sent to Google Analytics.
__utmz persistent 6 months from set/update Stores the traffic source or campaign that explains how the user reached your site. The cookie is created when the javascript library executes and is updated every time data is sent to Google Analytics.

Additional information available at https://developers.google.com/analytics/devguides/collection/analyticsjs/cookie-usage