Tinnitus is a phenomenon of the nervous system connected to the ear, characterized by perception of a ringing or beating sound (often perceived as sinusoidal) with no external source. This sound may be a quiet background noise, or loud enough to drown out all outside sounds. It is sometimes referred to as "the club disease" as many people get temporary tinnitus at loud clubs or concerts.
Tinnitus can be objective (the sound, e.g., a bruit, can be perceived by a clinician) or subjective (perceived only by the patient).