Use absolute as a noun or an adjective when you're so sure of something that you know it will never change. For example, a devout person's belief in life after death is an absolute; that person has absolute faith in the afterlife.
Absolute can also mean "without any doubt," as in the case of an absolute beauty — such as a glamorous movie star or a supermodel — or "without limits," such as a dictator who has absolute power over the people. Or, absolute can describe a final demand that must be met, such as the absolute conditions a person buying a home might present to its seller — it's the last step and can make or break the sale.