What could lucency mean on an xray?

Less dense. Lucency means an area on the xray is less dense than is typical. What it may be depends on where it is and exactly what it looks like. In the lung, it could be a bleb or bulla, but in a bone, it could be a bone cyst or other non bone lesion. You need to see your doctor and discuss the possibilities. Your doctor may need to call the radiologist who read the study for insight.