What does senile dementia mean?

Dementia. Loss of cognitive ability (ie dementia) that occurs in old age (senile). This could include alzheimers or multi infarct (from strokes).
Senile dementia. Is a dementia occurring in an older person.
Old fashion term. Senile demenia is now most likely alzheimers disease; as senile meaning old age, means dementia of old age. The most common form of dementia is ad, but in the oldest old is more likely a combo of ad and vascular disease of the brain.