There are two main types of deafness, sensorineural deafness and conductive deafness. It is possible to have a mixture of both types of deafness. Some people have deafness in one ear, known as unilateral deafness or both ears. Most deaf people can hear some sounds at certain frequencies and hearing aids can amplify these. Very few deaf people have no hearing at all.
Sensorineural deafness: This is a permanent form of deafness. It means that the inner ear (the cochlear or auditory nerve) are not working efficiently.
Conductive deafness: This is often a temporary form of deafness, but is can be permanent in some cases. It means that sound cannot pass efficiently through the outer and / or middle ear to the inner ear. It is often caused by blockages such as ear wax in the outer ear or fluid in the middle ear (known as glue ear).