Tinnitis is a symptom that affects millions of people around the world.  Its name comes from the Latin word meaning "ringing."  The most frequently experienced symptom with tinnitis is ringing in the ear, but sometimes other sounds, such as buzzing or humming can be heard as well.  The sound is percieved by the ear even when there is no external stimulus.  So in other words, even in a perfectly silent room, a person with tinnitis would still be hearing the ringing.  Although people of all ages can suffer from thsi conditoin,  it most commonly affects people who are over 50 years of age.

Tinnitis is thought to be caused from damage to the microscopic endings of the nerve in the ear responsible for hearing.  Factors that contribute to developing this condition include being exposed to frequent loud sounds (such as working around jet engines, going to loud rock concerts, working with jackhammers, guns, etc.).  There are also certain medications classified as "ototoxic" which can cause damage to the auditory nerve and sometimes the vestibular system.  Damage from these medications is cumulative.

Sometimes tinnitis can be temporary, such as a side-effect of certain medication, or caused by a buildup of wax that is pressing against the ear nerve in a strange way, but other times it can also be permament and/or with no known cause.

One of the best ways to prevent tinnitis is to always use ear protection (for example, ear plugs) when you're going to be in a loud environment.  This is part of the reason why rock musicians, DJs, and airplane pilots wear earplugs as a normal part of their work.