Which of the following conditions does the suffix -itis commonly refer to?

The suffix -itis typically refers to inflammation of a specific body part or organ. In the case of appendicitis, it denotes inflammation of the appendix, which is a small pouch attached to the large intestine. This condition is characterized by symptoms such as abdominal pain, tenderness, and sometimes fever, indicating an inflammatory response.

In contrast, the other options describe different conditions that do not primarily involve inflammation. Acid reflux refers to the backward flow of stomach acid into the esophagus, kidney stones are hard mineral deposits that form in the kidneys, and joint pain can be caused by a variety of issues, including injury or chronic conditions like arthritis, but it is not described specifically with the -itis suffix unless referring to arthritis itself. Therefore, appendicitis is the only option that correctly exemplifies the use of the suffix -itis to indicate inflammation.