Dimensions: A dimension in GA is generally a descriptive attribute of an object that can be given different values. Exit pages, screens and sessions duration, browsers are all example of dimensions appeared by default in Google Analytics.
Metrics: Metrics are the individual elements of a dimension which can be measured as sum, average or ratio. Page views, Pages/Sessions, and average session duration are examples of Matrics in Google Analytics
Sessions: A session is a period of time that user spends on your website, web page or app within a date range. Other terms data such as page views, events, users are associated with sessions.
Users: The users are calculated as total users who have has at least one sessions within a selected date range. Users include both new and returning users.
Page Views: Pageviews means a total number of pages viewed by a user. Repeated views of a single view are also counted.
Unique Page Views: Unique page views doesn’t count the repeated page views of the single page.
Pages/Sessions: Average page depth of pages/sessions is the average number of page viewed by the user during a session. Repeated views of a single page are counted.
Average Session Duration: It is the average length of a session on webpage, website or app.
Bounce Rate: Bounce rate is the percentage of single-page visit i.e. during a session duration a person visit your web page and left the website without going to any other page fro the entrance page.
New Sessions: This is the estimate of the percentage of the first-time visit. Returning users are not counted in new sessions. Generally, the are the users visiting your site the first time.
Goals: A goal is said to be completed when the user performs any specific action.
Conversions: Conversions are counted when the number of times goals have been completed on your website.
Campaign: It allows you to add more parameters to any URL of your website to get more information about your referral traffic.
Acquisition: This section in Google analytics tells you how you acquire users.
Behaviour: The data from Behaviour tab helps you to improve your content.
%Exit: The %Exit is the percentage of page views that were final page in the sessions.
Sources: Google, Yahoo, Bing, MSN
Medium: Direct, Organic, Paid, Referal, Social