What is Arthritis? Arthritis is not a single disease, but an umbrella clinical term used to describe joint pain or joint disease. It translates literally to "inflammation of the joint." While there are over 100 different types of arthritis and related conditions, the two most common and profoundly impactful forms are Osteoarthritis (OA) and Rheumatoid Arthritis (RA) . The Two Main Types Understanding exactly which type of arthritis you have is the critical first step in finding an effective treatment, as the causes are entirely different. 1. Osteoarthritis (The "Wear and Tear" Type) This is by far the most common form. It occurs when the protective cartilage—the slippery, shock-absorbing tissue that caps the ends of your bones—wears down over decades of use. As the cartilage deteriorates, the underlying bone begins to change. Eventually, cartilage disappears entirely, causing bone to grind directly agai...