Comprehensive and Detailed 150 to 250 words of Explanation From Palo Alto Networks Network Security Analyst Knowledge:

In a Palo Alto Networks environment, the Service column in a security rule defines the destination port used for the initial session establishment. If an application like web-browsing (which typically uses TCP 80 or 443) is running on a non-standard port like TCP 9000, the analyst must create a custom Service object for that port.

Using this custom service object in the security rule allows the session to be established on port 9000 while maintaining full App-ID inspection. This is critical because it allows the firewall to verify that the traffic is actually web-browsing and not a threat masquerading as a web service. Option A is incorrect because "application-default" would restrict the traffic to standard ports only. Option C (Application Override) is incorrect because it would disable Layer 7 inspection entirely, which is a significant security risk. By using a custom service with the correct App-ID, the analyst ensures that security remains granular and effective without disrupting non-standard business applications.