Webtrends Analytics Query Parameters Reference, October 2013
The Webtrends analysis process can generate and maintain parameters that support visitor profiling when you enable Visitor History in your profiles. These visitor-related parameters are stored in a Visitor History Table for each profile that has Visitor History enabled.
Because Visitor History parameters are handled by Webtrends, you should not use these parameters in META tags on your web pages.
Parameters that describe elapsed time periods in days are calculated as a complete 24-hour period. Thus, if a visitor visits for the first time at 1:00 on Monday, then any visit before 1:00 on Tuesday is considered as zero days since the first visit (WT.vr.fvd), even though the actual day is different.