Dementia may be a collective term wont to describe various symptoms of cognitive decline, like forgetfulness. It’s a symbol of several underlying diseases and brain disorders. Dementia isn't one disease in itself, but a general term to explain symptoms of impairment in memory, communication, and thinking. Symptoms include forgetfulness, limited social skills and thinking abilities so impaired that it interferes with daily functioning. Medication and therapies may help manage symptoms. Some causes are reversible.