Hearing loss is the inability to perceive the presence of a sound at normal hearing levels. This can be caused by a number of factors, including noise exposure, age, genetics, medications, trauma, and infections. Hearing loss varies across individuals.
An audiogram shows the results of a hearing test. The audiogram lists intensity levels on one axis and frequencies (pitches) on the other. There are 4 levels of hearing loss: mild, moderate, severe, and profound. A person with “mild hearing loss” will miss many parts of speech, which can cause communication difficulties.
Audiogram explained, Healthy Hearing (webpage)
