Compact bone or cortical bone is the dense, heavy, hard outer layer on every bone. It is rigid and strong. 

Spongy or cancellous boneis the lighter, less dense, lattice-like inner layer present in every bone. It is also known as trabecular bone and is more flexible than compact bone. 

Together, compact and spongy bone tissue serve several functions. They give the bones their structure and strength, support other tissue in the body, protect internal organs, and facilitate the attachment of muscles which enables movement. They are also involved in the formation of red and white blood cells.