Shinta, from the Mayo Clinic website :
What's the difference between arthritis and rheumatism? What is connective tissue disease?Arthritis is a condition involving inflammation or damage to the structure of a joint. There are many forms of arthritis, and each one is treated differently.
Rheumatism is an older term that describes nearly any condition associated with joint or even muscle pain. It doesn't indicate a specific disease but indicates any condition that causes pain, inflammation and stiffness in your joints and muscles. For example, both rheumatoid arthritis and bursitis are forms of rheumatism.
Connective tissue disease describes an illness in which a person's antibodies are directed against his or her own tissues. That is, you develop a reaction to some of your own tissues. The diagnosis of the different types of connective tissue disease — such as tendinitis or fibromyalgia — often requires the presence of several symptoms or findings. If you have few symptoms, a more specific diagnosis than connective tissue disease might not be possible.
Shinta, I hope you're not asking because someone you know has it.