Dementia is a term used to describe a group of symptoms affecting memory, thinking and social abilities severely enough to interfere with your daily life. It isn't a specific disease, but several conditions can cause dementia.
Though dementia generally involves memory loss, memory loss has different causes. Having memory loss alone doesn't mean you have dementia, although it's often one of the early signs of the condition.
Alzheimer's disease is the most common cause of progressive dementia in older adults, but there are a number of other causes of dementia. Depending on the cause, some dementia symptoms might be reversible.