is a condition in which the body's bones become weak
1 Osteoporosis is a bone-thinning disease that causes your bones to become thin and weak and increases the risk of breaking a bone A broken bone may occur from a minor event such as a fall from a standing height.2  Low bone mass, sometimes called osteopenia, is a condition and is not considered a disease. Osteoporosis is a bone-thinning disease that causes your bones to become thin and weak and increases the risk of breaking a bone A broken bone may occur from a minor event such as a fall from a standing height.