A disease is a pathological of a part, organ or system of an organism resulting from various causes such as infection, genetic defect or environmental stress and characterized by an identifiable groups of signs or symptoms.

It is a condition or tendency regarded as abnormal and harmful or any impairment of normal physiological function affecting all or part of an organism.

Disease, sometimes, includes injuries, disabilities, disorders, syndromes, infections, isolated symptoms, deviant behaviors and a typical variation of structure and functions.

Disease can be classified as: