Osteoid refers to:

Osteoid refers to young hyaline matrix of true bone in which calcium salts are deposited.

Bone is a connective tissue made of osteoblasts or bone cells. These cells secrete matrix osteoid which gets calcified after few days. The osteoblast along with trapped osteoid can be referred to as osteocytes or mature bone cells.

The other options are wrong since the smallest bone of the body is called stapes, the largest bone of the body is femur, and the membranous ossification of cranium is the characteristic way in which the flat bones of the skull are formed.