There's a whole site dedicated to VLJ's....
Found this using Google:
http://www.verylightjetmagazine.com/ They are defining it as a jet weighing 10.000lbs or less.
But in general. VLJ's are owner flown, very small jets. Bought as a replacement for Pipers ans Cessnas,
Wait... the Very Light Jet Magazine defines "Very" Light Jets as MTOW under 4500 kg. So this just excludes Cessna Citation single-pilot jets with 4700...4800 kg MTOW. But what is new about the "real" Very Light Jets?