Domain names can be registered for a pre-determined period which can span from 1 to 10 years depending on registrars. When this period has elapsed, it is possible to renew the domain name. When the domain name is not renewed by its owner, it falls back in the public domain.
In order to help owners not miss this renewal date, most registrars will grant a Redemption Grace Period (RGP). This redemption period locks the domain for the current owner and prevents any reservation from other users so that the owner can renew his domain name before it falls into the public domain. It is therefore precautionary measure to prevent the owner’s domain from being reserved by someone else.
For more information on this topic, please read our article "What is the redemption period?".