A forever stamp, as its name suggests, is a stamp that never expires or depreciates in value. It is used for first class postage regardless of the rate.
The forever stamp was a product of a proposal submitted by the US Postal Service that was submitted to the US Postal Rate Commission in May 2006. The proposal asked for the creation of a forever stamp that will be implemented starting 2007. Upon approval, the forever stamp was to be sold based on the rates for first class potage (about 42 cents during that time). The forever stamps would then be sold based on the value of first class postage at the time it is purchased.
Forever stamps have a number of advantages to the user. First of all, a consumer can buy a lot of forever stamps and stock up on it and use them until it runs out without worrying about it expiring or dropping in value especially since there is a possibility that the Postal Service will impose a limit to the amount of forever stamps that it can sell at one time. Additionally, as the postal rates change, a forever stamp will make it obsolete to buy small denomination stamps (those that cost cents) to add to old postage. This level of convenience makes forever stamps very attractive for consumers.
The Postal Service will also benefit from forever stamps because of the money it will get from the sale of forever stamps that will most likely not be used until the future.