Wound Poison

Wound Poison is a poison that is purchased from a poison vendor and applied to a rogue's weapons. Every time the rogue hits with the weapon, there is a chance (modified by the speed of the weapon) of the victim being poisoned for 15 seconds. The poison will reduce all healing effects on the victim by 50%. The effect cannot stack.

Proc Chances Under the PPM Model
As of patch 3.1., the proc chance of Wound Poison (along with Instant Poison was changed to a PPM model, normalized for 1.4 speed weapons. This results in the following proc chances per weapon speed per attack:

Instant Poison v. Wound Poison
It is generally accepted[says who?] that PVE Mutilate specced rogues should use Instant Poison on their MH, since they will have 3/3 Vile Poisons.

For PVE Combat rogues, hoewever, depending on gear and talents, Wound Poison may provide more poison damage than Instant Poison on the MH.

At low AP levels, Wound Poison's higher PPM rate will make the first option (WP + 3/3VP) produce more poison damage than the latter (IP etc). However, higher gear levels will provide enough AP for Instant Poison to scale up and overcome its low proc rate.

The AP point at which WP + 3/3VP loses out to IP + 4/5IP + 1/3VP can be theorycrafted:

Poison Damage per minute = Proc Damage * PPM (this is based on white weapon swings, but will scale evenly for yellow swings as well)

At level 80, given the two options above:
 * Wound Poison DPM = (1.20 * (231 + 0.04 * AP)) * (21.4)
 * Instant Poison DPM = (1.07 * (300 + 0.10 * AP)) * (1.4 * 8.56)

These two options will yield equal DPM at about 8,000 AP. Beyond that, the IP option yields more main-hand poison DPM (other things being equal).

It should be noted that this does not take into account the effect of Improved Poisons on off-hand application of Deadly Poison. Each Deadly Poison hit on a target fully stacked with Deadly Poison refreshes DP and applies the other weapon's poison. For this reason, the harder hitting Instant Poison should almost always be paired with Deadly Poison for long, steady state fights.

Source
Wound Poison is purchased from poison vendors. It is also available as a drop from selected mobs.