The term 'Pumping Organ' is a reference to the HEART, which is a five-letter word. The HEART is a vital organ in the human body that pumps blood throughout the body. It is responsible for providing oxygen and nutrients to the body's cells and removing carbon dioxide and other waste products. The HEART is made up of four chambers, two atria and two ventricles, and is located in the chest cavity. It is composed of muscle tissue and is responsible for maintaining a regular heartbeat.