Forever Purchase is a term used to describe the purchase of a STAMP or stamps that can be used indefinitely. It is a type of postage that does not expire and can be used for multiple mailings. The term is often used in reference to the United States Postal Service, which offers Forever Stamps that can be used for any domestic first-class mail regardless of the rate changes. These stamps are available in booklets or coils and can be purchased at post offices or online.