MEDICAL DEFFINITION: Gangrene: The death of body tissue due to the loss of blood supply to that tissue, sometimes permitting bacteria to invade it and accelerate its decay. It is caused by infection or ischemia, such as a thrombosis.EDICAL DEFFINITION: Gangrene: The death of body tissue due to the loss of blood supply to that tissue, sometimes permitting bacteria to invade it and accelerate its decay. It is caused by infection or ischemia, such as a thrombosis.