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.