Delirium: A rapidly developing, acute disturbance in attention and orientation that makes it very difficult to concentrate and think in a clear and organized manner.

Geropsychology: The field of psychology concerned with the mental health of elderly people.

Senile plaques: Sphere-shaped deposits of beta-amyloid protein that form in the spaces between certain brain cells and in certain blood vessels as people age. People with Alzheimer’s disease have an excessive number of such plaques.

Major neurocognitive disorder: A neurocognitive disorder in which the decline in cognitive functioning is substantial and interferes with the ability to be independent.

Neurofibrillary tangles: Twisted protein fibers that form within certain brain cells as people age. People with Alzheimer’s disease have an excessive number of such tangles.

Alzheimer’s disease: The most common type of neurocognitive disorder, usually occurring after the age of 65, marked most prominently by memory impairment.

Neurocognitive disorder: A disorder marked by a significant decline in at least one area of cognitive functioning.

Mild neurocognitive disorder: Neurocognitive disorder in which the decline in cognitive functioning is modest and does not interfere with the ability to be independent.