A URL category object is the object that the administrator should create to use as a match condition for the security policy rule that allows access to www.paloaltonetworks.com while denying access to all other sites in the same category. A URL category object allows the administrator to define a custom list of URLs that belong to a specific category, such as Business and Economy. The administrator can then use this object in a security policy rule to allow or deny access to the URLs based on the category1. For example, the administrator can create a URL category object that contains www.paloaltonetworks.com and assign it to the Business and Economy category. Then, the administrator can create a security policy rule that allows access to this URL category object and denies access to the predefined Business and Economy category2. References: Create a Custom URL Category, Create a Security Policy Rule to Allow or Deny Access to a Custom URL Category, Certifications - Palo Alto Networks, Palo Alto Networks Certified Network Security Administrator (PAN-OS 10.0) or [Palo Alto Networks Certified Network Security Administrator (PAN-OS 10.0)].

Explanation
Reference:
https://docs.paloaltonetworks.com/pan-os/9-0/pan-os-admin/policy/security-profiles

https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClomCAC