VPnP stands for Virtual Pen and Paper and is an acronym coined by Klingon Mage to describe the use of Neverwinter Nights with the DM client to run small-group adventures on a session-by-session basis, in the same manner that traditional pen-and-paper gaming is conducted. The characteristics that make a VPnP game would include:
A DM, who is usually (but not required to be) the author of the module.
A single party group, usually 6-8 players, sometimes more, sometimes less.
Games taking place on a regular schedule, as opposed to an always-on server (persistent world) where players come and go at will.