A bokken is a wooden sword used for training. The bokken is also known as a "bokto". The bokken represent a katana, and like a katana has a handle with enough space for two (ideally three) hands, a curved blade, generally with a thrusting tip. Different schools have different assumptions about the fine points of a bokken's shape. There is also an excellent MASE reference to bokken shapes
A bokken is different from a shinai; the shinai is flexible, split bamboo and is straight. The bokken is hardwood, solid and curved like a sword. These factors influence how they are used in training.
Bokken are used in various aikido schools, and in mugairyu; these tags are logical candidates for use with the bokken tag. Bokken can be used in solo practice Kata from Chiba Sensei, Saito-sensei, or in paired practice with a partner Saito-sensei (note: Saito is cited twice because he includes both solo and partner exercises.) Stenudd Sensei and Saotome Sensei. Iwama style aikido is particularly known for integrating weapons work early in training.
The bokken is a lethal weapon; it should be used with caution and due attention to safety.