A Grace Period is the time after a domain has expired that renewal is allowed, before the domain enters redemption at the registrar.
In General, once a domain has gone past it's renewal date, you no longer have a any rights to the domain, so a grace period is an absolute "last chance" for you to renew. In most cases, once your domain goes past the grace period, you should consider it lost. Domains do not simply become available again once they have reached the end of their grace period. A domain may be held by the registrar for 90 days (or longer) before a deletion request is processed with the registry. If a domain has been placed on "back order" it is very unlikely that you will ever be able to get hold of it, so it is important to make sure that you renew your domains before they expire.
ICANN Domains .com.net .org .info .biz
This also applies to .tv .in .ws .co .us and .me domains.
Domain will go offline immediately upon expiry and you have 30 days grace period within which to renew it. After this 30 days is up, the domain will enter the redemption period up to 90 days, wiithin which, you will be charged £50 Plus VAT if you want to re-activate the domain.
Nominet Domains .co.uk .org.uk .me.uk .ltd.uk
Domain will go offline 30 days after expiry and will be deleted after a further 60 days. Within the 60 day period you can renew without penalty.
Centralnic Domains .gb.com .gb.net .uk.com .uk.net .eu.com
These domains do not have a grace period. Domain will go offline immediately upon expiry and will enter redemption status at the registrar. You will be charged £50 Plus VAT if you want to re-activate the domain.
.eu Domains also do not have a grace period. It will officially expire on the second last day of the month the domain name is expiring on. The domain name will be deleted on the same day, if not renewed.