Super agility is the ability to have perfect balance and/or perfect equilibrium to a point far in excess to that of a normal human being in Earth's gravity.
Archangels have shown amazing reflexes in vessels, as shown by Raphael when Dean whipped an angel-killing blade at him and he caught it without turning around. Further, an archangel's dexterity is so great in vessels that they can execute heavy blows onto lesser beings without instantly killing them, as shown by Lucifer and Raphael.