What is the medical term meaning gently tapping the chest to determine underlying structures?

Percussion (per = through + cussion = strike) is tapping on the surface to determine the underlying structure. Percussion is a common diagnostic tool for the thorax (ribcage), and abdomen. The most common use is to tap out the edges of the liver during a routine physical exam. For the chest, it is used to diagnose pneumothorax (air in the chest/collapsed lung), emphysema and other problems.