Dynamic Address Groups: A dynamic address group populates its members dynamically using looks ups for tags and tag-based filters. Dynamic address groups are very useful if you have an extensive virtual infrastructure where changes in virtual machine location/IP address are frequent. For example, you have a sophisticated failover setup or provision new virtual machines frequently and would like to apply policy to traffic from or to the new machine without modifying the configuration/rules on the firewall.
https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-web-interface-help/objects/objects-address-groups