The "Visitor tracking" section of the Admin Portal uses a number of terms to display how people are interacting with your website. Here is a rundown of what some of those terms mean:
Visit: When someone visits the website, looks at one or more pages, and leaves without returning for some time. A single visit will usually encompass several pageviews.
Visitor: Someone who has visited your website. One person may be classified as multiple visitors if they use different devices to view your website, like a phone, tablet, and laptop. A visitor can make multiple visits.
Pageview: Any time a single page is loaded by someone and viewed.
Exit rate: Applies to specific pages only. It's the percentage of visitors who do not view any other page after this page. In other words, the percentage of people who viewed that page and then left the website.