Rheumatoid arthritis: An autoimmune disease characterized by chronic inflammation of joints. Rheumatoid disease can also involve inflammation of tissues in other areas of the body, such as the lungs, heart, and eyes. Because it can affect multiple organs of the body, rheumatoid arthritis is referred to as a systemic illness. Although rheumatoid arthritis is a chronic illness, patients may experience long periods without symptoms. Also known as rheumatoid disease.