Balance (Dex; Armor Check Penalty)
You can walk on a precarious surface. A successful check lets you move at half your speed along the surface for 1 round. A failure by 4 or less means you can't move for 1 round. A failure by 5 or more means you fall. The difficulty varies with the surface, as follows:
Being Attacked while Balancing: You are considered flat-footed while balancing, since you can't move to avoid a blow, and thus you lose your Dexterity bonus to AC (if any). If you have 5 or more ranks in Balance, you aren't considered flat-footed while balancing. If you take damage while balancing, you must make another Balance check against the same DC to remain standing.
Accelerated Movement: You can try to walk across a precarious surface more quickly than normal. If you accept a -5 penalty, you can move your full speed as a move action. (Moving twice your speed in a round requires two Balance checks, one for each move action used.) You may also accept this penalty in order to charge across a precarious surface; charging requires one Balance check for each multiple of your speed (or fraction thereof ) that you charge.
Action: None. A Balance check doesn't require an action; it is made as part of another action or as a reaction to a situation.
Special: If you have the Agile feat, you get a +2 bonus on Balance checks.
Synergy: If you have 5 or more ranks in Tumble, you get a +2 bonus on Balance checks.
*Includes any other surface that couldn't support the character's weight, such as a fragile branch.
Source: SRD 3.5 Combined Skills