Priority one

Priority one was a type of hail used within Starfleet that noted messages of high priority.

In 2268, Starfleet Command sent a priority one call to the USS Enterprise (NCC-1701) informing them that dilithium supplies had become dangerously low, but that they had found half of a map showing the location of a stolen dilithium shipment. 

In 2276, Starfleet Command sent a priority one signal, Security Condition Red, to the Enterprise ordering them to Starbase 22.