DPS means damage per second. DPS should never take gear that has defense rating, dodge rating, or parry rating on it. These stats are valuable for a tank, but are worthless as a DPS.
As a DPS you want stats that will boost your "DPS". Classes should focus on these stats to increase DPS:
Shaman (Elemental DPS): Spellpower/haste
Shaman (Enhancement): Attack power/haste
Hunter: Agility, ARP, Attack power
Death Knight: Strength
Rogue: Agility, Attack power, Armor Penetration (ARP)
Priest: Spell power & haste
Mage: Spell power & haste
Warlock: Spell power, haste, and crit
Warrior: Armor Penetration / strength
Druid: Armor Penetration
Tanks should gem stamina once they reach the defense cap of 540.