Categories of life

The categories of life was a system used to classify people on Earth after Miracle Day, in which people stopped dying. People were taken to overflow camps with Category Ones being secretly taken to modules and burned alive, since this seemed the only way Humans could die after the Miracle had come into effect. Since the formerly immortal Jack Harkness became mortal after Miracle Day, Esther Drummond joked that he was "category Jack". The Categories were arbiritary, as category ones could become category two's if they began to heal, such as Rex Matheson who should have been killed but then healed leaving a minor wound.

Category one
Those people designated as category one were brain dead and so were unable to function. In the overflow camps, category one patients were designated with a red clothes peg.

Category two
Category two contained those who had injuries that would continue to inflict pain or disable without causing damaged that would have previously killed. In the overflow camps, category two patients were identified with a blue peg and Rex was once such patient.

Category three
Category three referred to anyone who was healthy and so contained everyone not in categories one and two. (TW: The Categories of Life)

"Category Jack"
Category Jack as referred to by Esther Drummond to Captain Jack Harkness, because when the world became immortal, Jack previously immortal is now mortal.