The rotator cuff is a group of tendons and muscles in your shoulder. They form a “cuff” over the top end of your arm. It helps you lift and rotate your arm. And it keeps the shoulder steady as your arm moves.
A rotator cuff tear can be caused by different things. It can get sore from normal wear and tear over the years. This happens mostly to people over age 40. But you can also get one in a fall or by repeating the same activity over and over.