In Google Analytics:
- A visit is one visit session to a website via one computer or device. After thirty minutes of inactivity a new session starts. Visitor A could visit your site for 10 minutes go away for lunch and then look at your site for another 20 minutes. They then visit again the next day. That would count as three visits.
- A unique visitor is counted only once i.e. access via a given computer or device within the reporting period i.e. per day per week or per month. So if visitor A visited three times within a week (and the reporting period is a week) that would count as 1 unique visit for the week.
Visits will alway be higher than unique visits.