What is the medical term meaning loss of mental capacity?

The medical term for loss of mental capacity is dementia. Dementia is a general term for a decline in mental ability severe enough to interfere with everyday activities. It is not a specific disease, but rather a group of symptoms that can be caused by a variety of underlying conditions. Some of the most common causes of dementia include Alzheimer's disease, vascular dementia, Lewy body dementia, and frontotemporal dementia.