Bloody excellent. o_oWell, I think we went a little bit through this..A stab is a quick and simple movement that, if successful, are fatal strikes. It can be used to push back your opponent and disrupt your opponent's combo since its harder to defend against a stab than a slash. Also, the fact that stabs are quick and simple movements means that you do not leave yourself open for a fatal counter.
A lunge on the other hand, is what I used to think was a stab. It is quite similar to the stab in that it is the "thrusting" of your sword but it has alot more power in it and has much larger range. That is, you put your weight/momentum in the "stab" or jab/thrusting as you leap forward towards your opponent. Although this means that you can deal much more damage to your opponent, it is also much more risky than a stab as it leaves you open for potentially fatal counters.
xd Now, just demonstrate one.