The self zone is a system level zone and includes all of the routers IP addresses.
By default, traffic to and from this zone is permitted to support management protocols and control plane functions.
The management protocols could be telnet, SSH, SNMP, etc.
The control plane functions could be OSPF, EIGRP, RIP, etc.
After a policy is applied to the self zone and another security zone, interzone communication must be explicitly defined.