Lymph is a clear, watery fluid that circulates through the lymphatic system. It is formed from the interstitial fluid that surrounds the body's cells and contains white blood cells, proteins, and other substances. Lymph plays a crucial role in the immune system by carrying immune cells and waste products away from tissues and back into the bloodstream. It also helps to transport nutrients, hormones, and oxygen to cells, and remove toxins and waste materials. Overall, lymph is an essential fluid that supports the body's immune function and maintains fluid balance.