Some but not all tendons are covered by a sheath called the synovium
Synovium makes an oily fluid that lies between the tendon and overlying sheath helping the tendon move more freely and smoothly
Tendinopathy:
A term describing pain, swelling, and impaired function of a tendon, includes both:
Tendonitis - inflammation usually from injuries, overuse or strain
Tendinosis - chronic degeneration without inflammation. Tendon becomes thick and scarred. Usually due to failed healing of repeated minor injuries often with aging and associated with OA
Tenosynovitis:
Inflammation of the synovial sheath that surrounds a tendon
Some types of tendinopathy and tenosynovitis have characteristic symptoms and have their own name: