The Redemption Period is a policy started by ICANN and the Registry Operators. This is a 30 day Registry-imposed hold period for domain names which have expired and were not renewed by the registrant, allowing the drop domain process to run.
Normally domain names would be deleted at this point, but the redemption period provides the registrant with one last chance to recover the domain before it’s dropped and potentially registered by a new owner.
To renew a domain that is in the redemption period, there is a RGP (Redemption Grace Period) fee that is applicable, in addition to the regular renewal fees. It can take up to 4 business days for the process to be completed.
Alternatively, there is always the option of waiting out the entire redemption grace period which lasts for 30 days, following this period the domain name will be completed deleted and drop into the available domain pool approximately 5-6 days later. Once the domain name is deleted it is available to register by anyone, so the risk of losing it to a new registrant is high.