Dear manisha
Ply board is wood based panel product. It is formed by gluing and pressing thin sheets of veneers together usually an odd number of veneers with the grain direction of adjacent veneers running at right angle to each other. Block boards have a solid core made up of uniform strips of wood, each not exceeding 25mm in width and having thickness to match the thickness of the block board; these strips of wood are laid separately or spot glued or otherwise joined to form a slab. The core is glued between two or more outer veneers, with the direction of grains of the core blocks running at right angles to the direction of the grains of adjacent veneers.