|00:34The End Block is a big chunk of wood inside the bottom end of a stringed instrument that reinforces the joint where the sides meet. The end block also provides support for the end pin.
End Blocks are an integral part of construction of most acoustic stringed instruments, including those of the violin, guitar and mandolin (or lute) families. The blocks add structural integrity to the overall instrument. Instruments could be made without end blocks, but this area is so vulnerable to damage, it wouldn't be a good idea!