Definition of Disease Disease (Latin dis- = lack of, opposite of + ease = convenience, comfort) literally means lack of strength or satisfaction. It also means a person is no longer at ease. In medicine, disease means an impairment in structure or function of a certain body part or mind with identifiable symptoms.hat is Ischemia? Ischemia is the medical term for an inadequate blood supply to a specific area of the body. This results in a reduced oxygen supply as blood has difficulty in reaching the target tissues or organs.