What does it mean when a xray shows overlapping shadows?

Radiographs are. Shadowgrams - meaning everything in a view overlaps, which is why most require multiple views in different positions to be "complete". Usually, a radiologist can decipher the overlaps and understand what is happening, but sometimes is not sure and may say something like "... May be a nodule or due to overlapping structures.". Ribs and vessels are 2 things that can add up to mimic disease.