What is disease?
disease is A failure of the adaptive mechanisms of an organism to counteract adequately, normally or appropriately to stimuli and stresses to which the organism is subjected, resulting in a disturbance in the function or structure of some part of the organism. This definition emphasizes that disease is multifactorial and may be prevented or treated by changing any or a combination of the factors. Disease is a very elusive and difficult concept to define, being largely socially defined. Thus, criminality and drug dependence are presently seen by some as diseases, when they were previously considered to be moral or legal problems.
source: A GLOSSARY OF TERMS FOR COMMUNITY HEALTH CARE AND SERVICES FOR OLDER PERSONS. World Health Organization, 2004.