A request from one user, or IP address, for one or more web pages from your web site. Depending on how you're measuring the visits to your web site, one visitor may be counted as making multiple visits.
Often defined as a 'unique visitor', a person who visits your web site, one visitor may make more than one visit within a certain time frame.
The path that a website visitor takes, as they navigate through your site. A visitor path begins with the entry page, and ends with the exit page of each user's visit.
A visitor path is a very useful metric, because it can help you determine popular pages, popular paths to conversion, usability solutions, general visitor behavior from specific entry pages, etc. The knowledge gleaned from a visitor path can be very useful in improving the usability of a website.