A byoo is special type of
tack used to fasten the
head onto a
Taiko drum. It lends its name to any type of Taiko drum which has a tacked on head -
Byoo-daiko as opposed to
Shime-daiko which attach and tune their heads with rope.
If you need a mental image of what a tacked on drumhead looks like, think of a tambourine--it too has a tacked on head.