Parry is a skill that lets you sacrifice 0-51% of your attack speed in exchange for the chance to deflect incoming blows. It complements the dodge skill. If you successfully parry, you will get a chance to riposte. Parry’s effectiveness is influenced by how skilled you are with the weapon you’re parrying with, unless you’re using a shield, which always lets parry work at full skill level. You can parry with non-weapons if you are skilled in brawling.
Parry used to be equal to dodge in usefulness, back when instead of slowing you down, it reduced your attack skill, which unlike a loss of attack speed could be compensated for. Parry is currently a non-recommended skill unless you are aiming to be a defensive tank. Remember, the best defense is to kill the enemy faster!
The ingame help reads:
Skill duration: random. Type of skill : neutral skill. Affecting stats: Str/Dex. It uses no endurance points. While most of the art of combat leans towards the offensive side, a portion of this art leans also in the defensive direction. If one has a weapon in hand, even better if he has a shield, he can use these to help deflect blows aimed at himself. The best way to live to fight another day, is not to die. Of course, if one is spending time defending himself, he may not attack with the same effectiveness as he would if he was not holding himself back in order to defend himself. Usage: parry <0-51>