These two terms get bandied about quite regularly when talking about website statistics and analytics. They are related, but different. And just when we get it all straight in Google’s true nature, things change. As of April 2014, Google Analytics changed the way it refers to site sessions and visits. Site sessions are not visits and unique visits are now users.
The good news is that it appears just the terminology has changed in an effort to bring more consistency to the way Google Analytics names things across many platforms.
Visits (formerly site sessions) are a more robust engagement with your website, where users (formerly unique visits) can be as simple as clicking through to your home page and then leaving. Both have value, but one will tell you a bit more than the other.
According to Google, a visit (formerly session) is a group of interactions that take place on your website within a given time frame. For example, a single visit can contain multiple pageviews, events, social interactions, custom variables, and e-commerce transactions.”
Understanding visits and users gives you an idea of how many people are coming to your site and what they are doing when they get there. You can use this analysis to improve your site structure, content and optimization for SEO purposes.