Osteopenia means bone density that is lower than normal but not low enough to count as osteoporosis. It is best thought of as an early warning sign, not a disease — and it does not guarantee you'll go on to develop osteoporosis or break a bone.
It's found on a bone density (DEXA) scan with a T-score between -1 and -2.5 (see bone mineral density). Most people with osteopenia don't need medication; the main response is lifestyle — see osteopenia for what helps.