Theraband is rubber tubing or flat sheet-like elastic material that is made in a variety of resistances.  These are used for a multitude of exercises to promote stability and strength in your core, lower back, muscles around your shoulder blades and upper back.  A great way for you to continue your strengthening at home, and small enough to take with you to work or travel to ensure you can continue your home program no matter where you are.  Your Physiotherapist will prescribe one or more resistances, depending on your home program.