Heres the helpfile:

Exotic weapons have been known to permit a number of unusual combat techniques. These skills are not taught by any of the known adventuring guilds. Unless a mentor can be found, these are best learned by experimentation and diligent practice.
Swing: If successful, this technique knocks an opponent to the ground.
Lunge: If successful, this technique can cause bleeding.
Wallop: If successful, this technique can stun an opponent.
Batter: If successful, this technique can stun an opponent.
Rip: If successful, this technique can cause bleeding.
Project: If successful, this can unnerve or bewilder an opponent, as well as drain some mana.
Discharge: If successful, this can afflict the opponent with a minor malison, increasing the damage they suffer.
A warrior with the Hour Past Midnight legacy enjoys an advantage in using or defending against any of these exotic techniques. See also: EXOTICS

So you wield an exotic weapon that gives you RIP, you have that skill until you remove the weapon. You usually have it at 1% (50%) and have to use the skill to gain skill in it. The higher your %, the better the skill gets