A wood block is essentially a small slit drum made from a single piece of wood and used as a percussion instrument. It is hit with a stick and it makes a noise that sounds like "tock, tock."
Oriental musics use a variety of blocks ranging from small hand-held blocks to enormous (often immovable) "temple blocks" which may be sounded by swinging a large log against them.
Wood blocks are closely related to temple blocks and jam blocks