In web analytics, first visit / first session means an instance when users first landed on a website or page. It is a specific web analytics measurement defining unique hits and page views of first time visitors. This is important in getting the actual number of unique traffic that a website is getting. It will show how websites perform especially for those using the Internet as their business arena.
First Visit / First Session metrics however can only see web traffic. It does not measure quality user engagement while onsite. A separate web analytics metrics is usually used to generate reports on user sessions and onsite engagement. For example, the first visit / first session can report thousands of new unique hits for a website. It will provide hard data on web popularity but cannot offer intelligence on user behavior.
The first visit / first session metrics often get more complicated when returning or repeat visitors land on the web page. Less sophisticated web analytics tools could register this hit as another first visit. This means that if visitor A hits the website on day one and returned the next day, the analytics will generate 2 unique first visits. In reality, there is only one visitor that landed on the page on two separate instances.
To solve the matter, some high end web analytics tools capture the IP addresses of visitors. In this way, the identity of the computer from which the traffic originated can be determined. So, there would be no double counting of first visitors which is very valuable for accurate traffic monitoring.