What is the default action for firewall filters?

Each firewall filter in the JUNOS software contains a hidden term that causes a single final action for all filters. This final action is to discard all packets and can be interpreted as:
term
implicit-rule
{
then {
discard;
}
}
This term does not appear in your configuration, but is applied by the router on all filters.
The lack of any from match conditions results in all packets performing the defined action: the silent discard of those packets.
Many users configure this term within their filter for readability and to remember
that its actions always take place.