Tendons connect muscles to bones. When they get irritated and cause pain, it's called "tendonitis." (The "itis" part just means inflamed or painful.) The tendons in your wrist have to go through a very small "tunnel". Moving your hand can make the tendon rub inside the tunnel and cause tendonitis. Tendonitis in the wrist is very common, but pain may be caused by something else.

I hope I'm making sense!