Do you guys Know what the red thingy is called that is in the neck of frigate birds?

The great frigate is more coastal (they catch most of their food up in the air by robbing other seabirds). Both Great and Magnificent birds are large black birds. The males are identifiable by their iconic, red leathery throat pouch (also called "red gular sac") ... Magnificent males frigate have a purple sheen.

So it is the red gular sac

Males have gular pouches, which they inflate during mating season.