In Kingdoms of Amalur: Reckoning for the PC, PS3, and Xbox 360, you can parry an attack which will allow you to attack much quicker immediately after. Attacking right after a parry is what a riposte really is, so it’s not really a move in itself.
In order to parry, you use the block button, however you have to block at the right time. Holding block won’t cut it, you need to wait until an attack is about to land and block at just the right moment to perform a parry.
After you parry the attack, start attacking to Riposte. This is how you get the Riposte achievement/trophy as well, by doing this a total of 25 times.