Doctors might use the following terms a lot while briefing a particular condition. However, there is no reason to be confused as the following explanation will clear the cloud surrounding them:
Tendonitis: Tendonitis is a condition which occurs when a tendon gets inflamed and/or irritated. Usually the inflammation happens due to micro (small) tars in the tendon.
Tendinosis: Tendinosis is basically known as the chronic non-inflammatory degeneration of a tendon. This condition might develop due to chronic tendonitis or because of repetitive strain injuries to a tendon without sufficient time to heal.
Tendinopathy: Tendinopathy is sometimes used for describing a problem with a tendon. These issues can include tendinosis and tendonitis, inflammation of membranes around a tendon, as well as tendon tears.
It is the rule of thumb that when a tendon becomes painful, experts often assume it to be a case of tendonitis. Although, according to a research tendonitis is not as popular as tendinosis, which suggests that tendinosis is sometimes misanalysed as tendonitis.