What is a Forever stamp?

According to Stamps.com, Forever Stamps were created by the United States Postal Service in 2007. Forever Stamps are non-denominational first-class stamps that are valid indefinitely for letters or small packages that weigh 1 ounce or less.

Forever Stamps lock in postage rates. For example, in 2013, the rate of first-class postage was $0.47. In 2014, the postage rate for first-class postage increased to $0.49. Customers who purchased Forever Stamps in 2013 can still use them on letters that are sent in 2014; these stamps prevent customers from having to pay the 2-cent difference. This also applies to future postage rate increases.