Unique visitors = Unique users visiting your website. If I visit your website every day for a month, I count as one monthly unique.
Visits = Individual sessions to your website, in which I may access multiple pages in a specific time frame. If I visit your website once in the morning, and surf around a couple of pages on your site, that's one visit. If I return to your website eight hours later, that's a second visit.
Pageviews = The loading of an individual page. If I visit your website and click around to five different pages, that is five pageviews.
Hits = The loading of any file off of your web server. If I visit a webpage that has five images on it, then that counts as 6 hits ... one to load the HTML file, and five to load each individual image. This is the least accurate when trying to track your site's traffic but is useful to gauge your server resources as it's directly related to your bandwidth.
Thanks for these description but here I like to have your view on this...is like what would be the important things for you if you check any website stats, Is it Unique Visitors or Hits? you more emphasis on.
Traditionally, it was unique visitors and the all important pageviews. However, with the increased use of AJAX, where people can interact with webpages without actually loading multiple pages, pageviews is becoming more and more an inaccurate representation. For example, by using the Quick Reply editor, I am able to post this without ever loading a separate webpage from the page I visited to view this forum thread. A new statistic that is replacing pageviews is the amount of time spent on a website.