Turning undead is the ability to force back or to banish the undead. As this is typically granted through the power of religious faith, the rules text here will assume that a cleric is doing the turning. Certain creatures, being anathematic to undead, can also create this effect naturally.
These are the d20 target numbers for turning undead:
Turning undead takes one full round. The cleric must be within 60 feet (12 combat hexes) of the creature or creatures to be turned. During the turning attempt, the cleric cannot move or take any other action. Turning undead does not require concentration, however: if successful, the effect occurs just before the cleric’s next turn,
One turning check is made per attempt no matter how many undead are to be affected or what type(s) they are; the number is compared to the appropriate target for each creature. The maximum undead that can be affected is be one creature regardless of its HD (hereafter referred to as the “freebie”), plus 1 HD of creatures per level of the cleric. For example, zombies have 2 HD. A 1st level cleric can turn only one, and a 2nd level cleric can turn two (freebie + 2 HD of turning applied to the other one.) To turn 3 zombies at once, however, would require a 4th level cleric (freebie + 2 + 2 = 4).
A successful turn indicates that the cleric has literally lifted and hurled the creature back a distance of ten feet (2 combat hexes). What’s more, the creature is then considered stunned, as per normal stunning rules. The cleric can attempt to turn creatures again and again, driving them back into rooms, causing them to plunge from high places, even pushing incorporeal creatures through solid walls.
If the Turn Undead table shows a T, that type of creature can be turned automatically, regardless of the die roll’s result. If the Turn Undead table shows a D, that type of creature will be destroyed, instead of being turned. In both cases of automatic results, the 1 round of effort must still be expended.
Note that intelligent undead creatures can choose to flee – dissipating if possible, or simply running away if not. All such undead, being sensitive to holy power, will retreat the moment they encounter a cleric that is able to turn them automatically; if the cleric must roll a die, the creature must succeed at an Intelligence check in order to flee.