Hearing is the ability to detect sound. The outer ear, pinna and ear canal "catch the sound" and direct it toward the tympanic membrane (ear drum). The sound vibrations pass through the middle ear, an air filled space behind the ear drum, via the ossicles (bones of the middle ear). This vibration is passed on to the cochlear which stimulates the auditory nerve to the brain.
A hearing test assesses how loud a sound has to be before you can detect it