Sessions: A session consists of a series of pageviews that a single user makes during a period of activity. The session ends after the user either closes the browser, clears cookies, or is inactive for 30 minutes.
Users: A person who interacts with an app or site whose activities you measure with Google Analytics.
New User: Users who have never been to your site, according to Google’s tracking snippet
Returning Users: Users who have visited your site before.
Pageviews: A pageview (or pageview hit, page tracking hit) is an instance of a page being loaded (or reloaded) in a browser. Pageviews is a metric defined as the total number of pages viewed.