A black tag in triage means that the patient is either dead or will die regardless of the treatment that the hospital or EMS provides.
Black Tags in EMS or Hospitals are used for the deceased and for those whose injuries are so extensive that they will not be able to survive given the care that is available.
In EMS code black means that the patient has expired.
When a patient expires it means the patient has died and they call it as a code black and there's nothing that they can do to revive the patient.
Sometimes a paramedic may call code black if the patient is gonna die regardless of what they do.
Or if a patient has a DNR order which means they cannot try to save the person so if the EMS shows up because someone called for them then they have to let the person die.
Other codes that paramedics use are Code green. Non critical patient. Code yellow. Potentially serious. Code red. Serious/critical injuries. Code blue. In or near arrest and then code black which means the patient died.
In a hospital setting a hospital may use code black to refer to a bomb threat but for EMS it means death in a patient.