What it means? It means that they aren't hearing normal breathing, shallow, drawing less breath. When you put it together: Diminished means less. Breath sounds are breath sounds. Auscultation is listening (heart, abdomen, lungs) and a part of normal physical evaluation. So, less than normal breath sounds upon listening. If you check out the link below it is a library of normal and abnormal findings during auscultation.
www.cvmbs.colostate.edu
www.cvmbs.colostate.edu