The word dementia is an umbrella term that refers to many different diseases. Different types of dementia are caused by different physical changes to the brain. Some dementias are reversible, meaning that they can be treated and cured. Some are irreversible, meaning that there is no cure yet.

Dementia is not a specific disease. Many diseases can cause dementia, including Alzheimer's disease, vascular dementia (due to strokes), Lewy Body disease, head trauma, fronto-temporal dementia, Creutzfeldt-Jakob disease, Parkinson’s disease, and Huntington’s disease. These conditions can have similar and overlapping symptoms. 

Dementia is an overall term for a set of symptoms that are caused by disorders affecting the brain. Symptoms may include memory loss and difficulties with thinking, problem-solving or language, severe enough to reduce a person's ability to perform everyday activities. A person with dementia may also experience changes in mood or behaviour.