Bokken (木剣, "wooden sword") is the Japanese term in kenjutsu for a katana shaped out of wood. Used to train samurai in feudal Japan, it is now used as a training weapon in various Japanese sword arts. Some other martial arts (and all pedants) call it a bokuto (木刀, "wooden sword").
A suburito is a bokken designed for suburi. Suburi, literally "bare cutting", are solo cutting exercises. Suburito are thicker and heavier than normal bokken so that you have to develop either good technique, strong muscles or both to wield one. Their weight does however tend to make them poorly balanced, consequently they are not used for paired practise.
Miyamoto Musashi was famed for his use of the Bokken