Hit 

A request to the web server for a file. This can be an HTML page, an image (jpeg, gif, png, etc.), a sound clip, a cgi script, and many other file types. An HTML page can account for several hits: the page itself, each image on the page, and any embedded sound or video clips. Therefore, the number of hits a website receives is not a valid popularity gauge, but rather is an indication of server use and loading.

Pageview

A pageview is an instance of a page being loaded by a browser.

Unique Visitors

Unique Visitors represents the number of unduplicated (counted only once) visitors to your website over the course of a specified time period.

Bounce Rate

Bounce rate is the percentage of single-page visits or visits in which the person left your site from the entrance (landing) page. Use this metric to measure visit quality – a high bounce rate generally indicates that site entrance pages aren’t relevant to your visitors. The more compelling your landing pages, the more visitors will stay on your site and convert. You can minimize bounce rates by tailoring landing pages to each keyword and ad that you run. Landing pages should provide the information and services that were promised in the ad copy.