(from the Greek osteon – bone and poros – pore, hole) – a decrease in bone density as a result of a decrease in the amount of bone substance or insufficient calcification, can be limited to a section of bone (local osteoporosis), take over one or more bones as a whole (regional osteoporosis), all bones of the limb (widespread osteoporosis) or the entire skeletal system (systemic osteoporosis). It develops in old age, as well as as a consequence of bone atrophy with prolonged immobilization, fractures and inflammation of bone tissue, with various diseases caused by metabolic disorders, blood circulation, nervous and hormonal regulation.