Firewall Default allow
Default allow is a type of firewall ruleset in which the default condition of the firewall is to allow ALL connectivity - from anywhere, to anywhere. A default allow firewall with no additional rules loaded is effectively the same thing as no firewall at all.
Default allow firewalls are not recommended, because there is a race condition problem - a window of time in between a reset of the firewall to default rules and the re-loading of the extra rules to restrict access in which "anything goes." See Default deny.