Hit Defined Technically - Each file request sent to server while browsing a page is an individual hit. Or alternatively a "hit" is defined as "The access of a file by a user on a server". A visitor to a webpage in a single visit may produce one or dozens of hits on server, depending on how many graphics or other elements there are on your webpage.
Visits Defined Technically - A visit happens when someone - human visitor or bot visits your webpage. The visit can have one or more number of pages and also visitor or robots can visit a page multiple times.
Pageviews Defined Technically - A pageview is each time a visitor views a page on your website. A single pageview can generate quite a number of hits. As pages are comprised of files every image, css in a page is a separate file. So when a visitor looks at a page, they may see numerous images, graphics, pictures etc. which generates multiple hits.