https://live.paloaltonetworks.com/t5/blogs/what-are-applications-and-services/ba-p/342508# A service on the Palo Alto Networks firewall is a TCP or UDP portes which port is open or closed and does not look beyond Layer 4. An application it goes into Layer 7 inspection to ascertain which application is active in a data flow and will enforce "normal" behavior onto it, DNS Query
https://live.paloaltonetworks.com/t5/blogs/what-are-applications-and-services/ba-p/342508#
Concept 1
A service on the Palo Alto Networks firewall is a TCP or UDP port, as it would be defined on a traditional firewall or access list. It simply defines which port is open or closed and does not look beyond Layer 4.
Concept 2
An application is what makes the Palo Alto Networks next-generation firewall so powerful; it goes into Layer 7 inspection to ascertain which application is active in a data flow and will enforce "normal" behavior onto it (e.g., a session identified as DNS that suddenly sends an SQL query is abnormal and will be blocked).