What is the function of a "Service" object in a Palo Alto Networks firewall configuration?

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

While Palo Alto Networks firewalls are famous for Layer 7 App-ID inspection, they still require Service objects to define the Layer 4 (Transport Layer) parameters of a connection. A Service object defines whether the traffic is TCP or UDP and specifies the Destination Port.

A core objective for an analyst is managing these objects to maintain security. For instance, when creating a Security rule, an analyst can set the Service to application-default, which tells the firewall to only allow the application on its standard ports. However, if an internal application uses a non-standard port, the analyst must create a custom Service object for that specific port. This ensures that the firewall's state engine knows which ports to open for the session. Service objects can also be grouped into Service Groups to simplify policy management, allowing an analyst to update a single group object rather than editing multiple individual security rules.