Arthritis does not refer to one specific disease.  It is better to think of this disorder as a number of different, but related conditions.  Arthritis is simply defined as inflammation of the joints (the term has a Greek origin - arth means joint, and itis means inflammation).  The various types of this affliction share some common symptoms, such as joint pain, swelling, stiffness, and limited range of motion.  However, their causes, treatments, and prognosis can vary widely.  For example, gout and osteoarthritis sometimes have similar symptoms.  Their causes and treatments are very different, though.  It's important to talk to your doctor and get a proper diagnosis for any type of arthritis.