The full name of the event is Kokufu Bonsai-ten (国風盆栽展). Loosely translated, Kokufu Bonsai-ten means National Bonsai Exhibit.
国 (koku) = country
風 (fu) = customs or manners, among many other definitions
盆 (bon) = tray
栽 (sai) = planting
展 (ten) = exhibit
Robert J. Baran provides up-to-date information about the exhibit at:
The Nippon Bonsai Association has more information about the event on their website: