Final answer:
Osteopenia is a condition characterized by mild thinning of the bone mass and reduced bone density, but it is less severe than osteoporosis.
Step-by-step explanation:
Osteopenia is a condition characterized by reduced bone mass of lesser severity than osteoporosis. It refers to mild thinning of the bone mass where the formation of new bone is insufficient to offset normal bone loss. Osteopenia is not as severe as osteoporosis, and it represents a low bone mass.
For example, in osteoporosis, bones become weak and brittle, which increases the risk of fractures even with minor stress. In contrast, osteopenia represents a milder form of bone loss where the bone mass is mildly thinned but not to the same extent as in osteoporosis.