The riposte is sometimes called "the echo of the
parry" because, like
an
echo to an actual sound, the two are linked so finely they cannot
be separated. Too, like an echo, the riposte springs instantly from
its source.
The riposte is a counterattack launched after a successful parry
has been made. It is, in fact, the most common form of counterattack.
But it is a counterattack that forbids, generally speaking, the use of
the lunge. This is due to the fact that your opponent has already
atacked, has lunged himself and is close enough to be hit without generating
another such move.
According to the conventions of the foil, once a defending fencer
has performed a parry that has deflected an attacker's blade away from
his valid target area, he is granted the right-of-way that the attacker
initially possessed. He may then consequently attempt his own offensive,
or more precisely, counteroffensive action--the riposte.
But, as has already been mentioned, the riposte, to be legitimate, must
be delivered immediately after the parry, without hesitation. Any
pause may end up nullifying your priority in the exchange taking place.
From The Art and Science of Fencing, by Nick Evangelista