Tendonitis is defined as:

Tendonitis refers specifically to the inflammation of a tendon, often occurring at the site where the tendon attaches to the muscle. This condition is commonly a result of repetitive motion or overuse, and it is characterized by pain and tenderness at the affected area. The definition captures the essential aspect of tendonitis, highlighting the inflammation at the tendon-muscle junction, which is critical for understanding both the pathology involved and the general management of the condition.

Other options describe different structures or conditions: inflammation of joint structures aligns more with arthritis, while a tear in the tendon signifies a more critical injury, like a tendon rupture. Additionally, inflammation of muscle coverings at a joint pertains to conditions related to the fascia or membranes surrounding muscles, not specifically targeting the tendon itself. Understanding these distinctions is important for accurate diagnosis and treatment in medical administrative practice.