Arthritis is the failure of articular cartilage (the shiny covering over the ends of your bones).
There are two major categories of arthritis:
Osteoarthritis is the most common type and is due to abnormal wear and tear of the cartilage. This can be from an injury or excessive weight across your joints.
Inflammation is a disease of the immune system and affects the lining of the joint more than the cartilage. Examples of an inflammatory type of arthritis include Rheumatoid Arthritis, Psoriatic Arthritis, and Gouty Arthritis.