This statement comes from a Supreme Court decision in 1974:
"The impediment that an absolute, unqualified [executive] privilege would place in the way of the primary constitutional duty of the Judicial Branch to do justice in criminal prosecutions would plainly conflict with the function of the courts under Art[icle] III."

Source: http://www.infoplease.com/us/supreme-court/cases/ar41.html

What is the "absolute privilege" to which this decision refers?

Question

This statement comes from a Supreme Court decision in 1974:
"The impediment that an absolute, unqualified [executive] privilege would place in the way of the primary constitutional duty of the Judicial Branch to do justice in criminal prosecutions would plainly conflict with the function of the courts under Art[icle] III."

Source: http://www.infoplease.com/us/supreme-court/cases/ar41.html

What is the "absolute privilege" to which this decision refers?