The quarantine or grace period is often described as RGP phase (redemption grace period)What is the relation to domains?
.de domains that has been deleted, are then in quarantine for 30 days (.eu domains for 40 days). During this period the domains can not be found and may not be opened in the browser. In addition the previous owner (or a third party selected by the owner) can decide at that time if they want to undelete it. This quarantine is to ensure that unintentionally deleted domains may be brought back again. Unfortunately, it happens all the time, that domains are deleted due to carelessness.
This grace period method for .de domains exists only since 2013 and was set up by DENIC.
Domains will get in these quarantine, if they are deleted accidentally or intentionally.
RGP is the shortcut of "Redemption Grace Period". This is another word for the term quarantine or grace period (partialle also called cooldown).
In this period are domains that have been deleted. It could also happen that contracts aren't renewed with the providers and the domains are therefore automatically deleted.
In the RGP-phase the domains could not be opened in the browser (this is suitable at .de and .eu domains). However the domain owner can undelete the domain. If it stays at the deletion of the domain, it can be catched and registered after the quarantine again.