The organ used to hear is the ear. The human ear comprises several parts: the outer ear (pinna), the middle ear (ossicles), and the inner ear (cochlea). Sound waves enter through the outer ear, causing vibrations in the eardrum, which then transfer to the ossicles. These vibrations are converted into nerve signals in the cochlea and transmitted to the brain via the auditory nerve. The brain interprets these signals as sound, allowing us to perceive and respond to various auditory stimuli.