Unique Users - Users marked by either a GUID (Global User ID) or a cookie in the form of an ID that is attached to a user's browser. Unique users do not include repeat users during a specified session.
Unique Visitor - Unique Visitor is a user who visit your site once in 24 hours or in some other specified period. Using this you will know how many people visits your site, but not how many pages.
URL (Uniform Resource Location) - The address of any resource on the Internet that is part of the World Wide Web. For example: www.yutrend.com.