A genetic, non-inheritable disorder caused by osteoblastic differentiation defects that result in the replacement of bone marrow and trabecular bone by fibrous stroma and immature bone. It usually affects a single bone and less frequently multiple bones. Skull, femur, tibia, and humerus are the most frequently affected bones. It manifests with pain, deformities, and fractures. The disease is fibrous dysplasia (MONDO_0000845, a Monarch Disease Ontology term). Also known as: fibrous dysplasia of bone.