Mature osseous connective tissue (bone) is composed of collagen fibers and mineralized matrix. When osseous CT is first made, the osteoblasts secrete osteoid onto which calcium salt then precipitates. What is osteoid?

Osteoid is the immature unmineralized bone.

Explanation:

Osteoid is the unmineralized bone and makes the organic part of the bone matrix. In general, one-third of the bone matrix is osteoid. Osteoid includes ground substances such as proteoglycans and glycoproteins. Osteoid also has collagen fibers. Both ground substances and collagen fiber of osteoid are secreted by osteoblasts.