What do the different metrics (visits, page views, unique visitors, etc.) mean in Analytics?

Here are definitions of metrics used in Siteimprove analytics:

• % of total page views: this is the number of page views as a percentage of the total page views to the site and/or to the selected group.
  
• Average page views: Calculated by dividing the number of page views by the number of visits
• Bounce Rate: Your Website's Bounce Rate is the percentage of people who land on one of your web pages and then leave (bounce) without visiting another page. Bounce rate is calculated from single-page visits divided by the total number of visits on the site. Learn more about bounce rates.
• Page Views: A page view is a count of how many times a page has been viewed on a website or the chosen group within the chosen period of time. All page views are counted no matter how many times a user has visited the website in the chosen period of time.
• Referrals: A referral occurs when one website source links (refers) to your website, and the user clicks through to land on your website
• Returning Visitors: A returning visitor is a user that has visited your website during the period selected, who has also visited your website at least one time prior to this period. So if you have 10 unique visitors on your website in January and five of them have been on your website in a period prior to the period you have selected, then you will have five returning visitors. Similar to unique visitors, this metric relies on cookie data, so treat this metric with the same caution and look at trending rather than absolute values.
• Unique Visitors: Unique visitors are identified as unique visitors if they did not have a persistent or session cookie from Siteimprove on their browser/device. Treat this metric with caution and look at trending rather than absolute values. Cookies are specific to browser and device which means that if a visitor is visiting your website using a different browser or device than before, or has deleted or never accepted the cookie, then that person will be seen as a new unique visitor even if that is not the case.
• Visits: A visit is defined as a series of page requests from the same uniquely identified visitor with a time of no more than 30 minutes between each page request
• Visits | % of Total: See: Why does the sum of the % of total visits add up to more than 100%?

Info: For Traffic Sources definitions such as Referrers, Social Media, Search Engines, External Search Terms, Direct Traffic, see How are Traffic Sources defined in Analytics?