This sounds interesting, I'll have to look these up when I get home from work. In fencing, riposte is simply to return the steel. Fencer B parries Fencer A's attack, then he in return attacks Fencer A.
A ------> B (A attacks B)
B <------ A (B parries A (above) then he ripostes (attacks the attacker back)
Or, for you theatrical fencing choreographers, this is an example of how it's written out for a play or movie fight:
Fencer 1 ------------------ Fencer 2
Thrust to Flank --------> Parry 2
Parry 3 <------------------ Riposte w/ Outside Cheek Cut
I'll have to see how this feat works.