What is lymph?

Clear fluid: It is a fluid (usually clear) that circulates between the tissues of your body. It is fluid not in the arteries and veins. It contains some proteins and white blood cells.

Tissue fluid: Arteries and veins carry blood cells and a serum, some of which leaks out from capillaries and bathes your tissues. It gradually accumulates and is collected in lymph channels which empty back into the heart. It traverses nodes (lymph nodes) which can be the first line of defense against infection and cancer. When blocked, like after lymph node dissection, it can accumulate causing lymphedema.