Arthritis is an inflammation of one or more joints in the body. An affected joint is usually warm, swollen, and painful, and movement is often difficult or uncomfortable.

There are many different types of arthritis which have similar symptoms, but different causes. Some of the most common types of arthritis are:

Reference 9A: Merck official website
(Source: http://www.merck.com/disease/arthritis/about/home.html)