condition: a general term for diseases, lesions and disorders; often excludes mental health, where disorder is preferred (eg Diagnostic and statistical manual of mental disorders)

disease: a condition that impairs the normal function of a person, plant or animal. Diseases can be communicable (spread to a person from an animal, the environment or another person – eg measles, HIV, malaria, influenza) or noncommunicable (caused by environmental or genetic factors – eg cardiovascular diseases, cancer, diabetes, chronic respiratory diseases)

disorder: a synonym for disease (ie a functional abnormality), used for noninfectious conditions such as physical, metabolic or mental conditions; in mental health, mental disorder is preferred to mental illness

illness (sickness): a synonym for disease but often used to indicate the person’s experience of a disease (ie a person can have a disease without being ill or sick)

syndrome: the occurrence of several associated medical signs, symptoms or other characteristics (eg Down syndrome)

See also Disease names