A heating pad is a flexible, fabric-covered device containing heating elements (electric, chemical, or microwavable fillers like gel/grains) used for applying warmth to the body for pain relief, muscle relaxation, and to ease stiffness, functioning through thermotherapy by increasing blood flow. 

Electric versions often have adjustable temperatures and timers, while microwavable ones use natural materials for contoured relief, all aiming to soothe discomfort from issues like cramps or soreness, but require safe usage to avoid burns or other risks.