An audiogram is the result sheet of a hearing test (pure-tone audiometry). The horizontal axis shows frequencies from low to high tones, the vertical axis shows loudness in decibels. A curve is drawn for each ear, representing your individual hearing threshold. The lower the curve, the better you hear in that range.
During the test you sit in a quiet booth with headphones. You hear tones of varying pitch and volume one after another and press a button as soon as you notice a sound. This is often complemented by a speech test (understanding words) and bone conduction to narrow down the type of hearing loss. The test is painless and usually takes only a few minutes.
An audiogram makes sense if you struggle to follow conversations in noisy places, turn up the TV, frequently ask people to repeat themselves, or notice ringing in your ear (tinnitus). It is also standard before fitting hearing aids and in cases of occupational noise exposure.
Make sure the test is carried out professionally by ENT specialists or hearing-aid acousticians using calibrated equipment in a quiet environment. A single test is only a snapshot; if results are unclear, a second measurement is worthwhile. Costs depend on the provider, the scope and whether a doctor has prescribed the test.