From the time the first web page was posted, its authors wanted to know: How popular is this page? At first, it wasn't so easy to tell how many unique visitors had frequented a site in a given time frame, so early webmasters resorted to simply measuring a) how many times a page was accessed; or b) how many (and which) files were accessed in a given time frame. These figures resulted in the ambiguous term "hits" which is only a very rough measure of how popular a page/site is and how many people visit it.
These days, it is possible to get a more exact accounting of how many visitors (unique sessions) a site has received in a given time frame, how long they were on site, what pages they viewed etc.
But, sigh, there are still a lot of people who persist in describing a site's activity by the number of "hits"...