What is the difference between dementia and Alzheimer's?

Dementia is not a disease per se; it's a set of symptoms that affect daily functioning (such as memory loss and changes in abstract reasoning and attention) caused by deterioration in the brain. Alzheimer's disease is the most common cause of dementia. Sometimes the two terms are used interchangeably, often by those who find "Alzheimer's" to be a stigmatizing word. But technically they are not the same thing. Dementia is the broader, umbrella term; there are many different causes of dementia (disorders that feature dementia): vascular dementia; Parkinson's Disease dementia; Lewy Body Dementia; frontotemporal dementia. Alzheimer's is just one type of dementia. Dementia can also feature in other brain disorders such as Huntington's Disease and AIDS.