Deafness and hard-of-hearing are not the same thing. Deafness means a total or near-total loss of hearing, along with an inability to understand speech. A person can be born deaf, or be born with normal hearing and become deaf because of an accident or illness.
People who lose some ability to hear during their life are called hard-of-hearing. These people can hear and understand some speech if it is loud. Children who are born deaf or who are hard-of-hearing have problems learning to speak because they cannot hear to imitate the sounds other people make.
Poor hearing is sometimes the result of things which might have been avoided. Severe infections such as measles, tonsilitis, and mumps may bring on poor hearing if they are not treated promptly. Sometimes, poor hearing is caused by sound itself. If a person continuously hears loud explosions or violent vibrations, a loss of hearing may take place.
Many deaf people have “hearing ear dogs” who have been trained to warn their masters of doorbells ringing, alarms sounding, and babies crying!