Access control rule blocking actions
A block action is an access control rule action that denies network traffic without further inspection and prevents the use of file, intrusion, or network discovery policies for blocked traffic.

Block and Block with reset actions immediately stop traffic from entering the network. Block with reset rules reset the connection except for web requests met with an HTTP response page. The HTTP response page is used to notify users when their web request is blocked, but it cannot be displayed if the connection is immediately reset.
For more information, refer to HTTP response pages.