Registrants offer the domains for the consumer to own for certain period of time. The consumers have to renew it before the expiry time to continue the ownership. If the owner fails to renew the domain, it will get deleted and moves to the master list from where anyone can buy it.
But the registrants will keep the domain on hold for a period of 30 days allowing the original domain owners to retrieve their domain. This retrieving period of 30 days is knows as redemption period which gives some extra time for the owners to renew their expired domain.
During redemption period, the domain will be deleted from the Zone file in the global DNS. Therefore, the website or email service for using the domain will stop working and stays off line.
Five day period after the redemption period of 30 days is Pending Delete Phase. During this Phase, neither the owner can renew the domain nor it will be available to the public for fresh registration. Only after Pending Delete Phase, the Registry will add on the domain again in the master list for new registration.
The domain owners have to pay some extra fee to retrieve the domain during redemption period. So it is good to renew the domain before its redemption period to avoid problems.