A disease is a malfunctioning of a particular part of a living thing. Diseases usually have a set of specific signs and symptoms, and often a specific cause like a viral or bacterial infection. Diseases are usually something for which medical treatment is given by doctors or other trained professionals.
Politics of disease description
The classification of whether or not a particular set of symptoms is a disease has often been controversial. Often those with the condition have to lobby to get medical recognition or treatment. On the other hand, there are a number of diseases and conditions which people consider to just be part of the range of human function: "neurodiversity" advocates claim, for instance, that autism and Asperger's Syndrome, despite being cases of atypical brain function, should not be considered medical issues. This affects the field of mental health also - homosexuality was removed from the Diagnostic and Statistical Manual of Mental Disorders (the DSM) in 1973 is an example of the demedicalisation of a practice.