What is Persona Designata?

Legal Definition
The persona designata doctrine is a doctrine in law, particularly in Canadian and Australian constitutional law which states that, although it is generally impermissible for a federal judge to exercise non-judicial power, it is permissible for a judge to do so if the power has been conferred on the judge personally, as opposed to powers having been conferred on the court. The doctrine in the more general sense has been recognised throughout the common law countries (including the United States). Persona designata, according to Black's Law Dictionary, means "A person considered as an individual rather than as a member of a class", thus it may be a person specifically named or identified in a lawsuit, as opposed to the one belonging to an identified category or group. While it has its origin in Montesquieu's doctrine of the separation of powers, it can be traced back as far as Aristotle's Politics.

In Australia the doctrine is considered to be an exception to the Boilermakers' doctrine of separation of powers, which holds that conferral of non-judicial power which is not incidental to the exercise of judicial power on a Chapter III court (a federal court) is unconstitutional.
-- Wikipedia
Legal Definition
A person pointed out or described as an individual, as opposed to a person ascertained as a member of a class, or as filling a particular character.
-- Black's Law Dictionary