Meaning – The term outbound, refers to data that is sent to the network. In the view of a server firewall, inbound means another server or client in front of the wall, initiate a connection with own server. Inbound refers to traffic initiate from external. Outbound refers to traffic initiate internally.
Inbound firewall rules define the traffic allowed to the server on which ports and from which sources. If no inbound rules are configured, no incoming traffic is permitted. Outbound firewall rules define the traffic allowed to leave the server on which ports and to which destinations.
Example of usage – “Incoming and outgoing are from the perspective of the machine in question. Incoming refers to packets which originate elsewhere and arrive at the machine, while outgoing refers to packets that originate at the machine and arrive elsewhere.”