What us a difference between a chest xray and a lung xray?

X-ray: Not much. If it's a plain x-ray , a chest film shows the lungs. If they did a pa & lateral(front and side view), they get a better look at everything, but i've never heard it called a lung x-ray. Whenever a radiologist reads an x-ray , they look at everything in the film , not just lungs. Many times things are found that weren't part of the reason the test was ordered. There are lung scans.

Probably not much: Chest xray includes heart, lungs, mediastinum, bones shoulders, and upper abdomen. The lungs are definitely visualized. For more detail imaging of lungs, sometimes high resolution CT imaging of chest may be performed.