Indecisive is a role modifier that restricts a power role from using its ability on the same target two nights in a row. Even if the ability is blocked or otherwise prevented, its user still cannot pick the same target for the ability the next night. Likewise, if the ability is redirected or deflected, the role's original target cannot be repeated the next night, but you can intentionally aim at someone you inadvertently aimed for the previous night.
Sometimes, Indecisive players are allowed to self-target (but still not twice in a row); the built-in limitation of Indecisive means that self-targeting is less useless than it normally would be.
This modifier is considered Normal on mafiascum.net. (The Normal version does not allow self-targeting.)
Use and Power
This modifier is most commonly seen on protective roles like Doctor as a method of preventing them getting out of control if a particularly strong target is identified; as such, it serves mainly as a method of reducing the swing of roles which are hugely more useful on some targets than others (a Doctor is strongest when protecting a Cop). It's around twice as strong as Non-Consecutive Night, because it allows for the ability to be used every night as long as the target is not repeated. It could also plausibly be used on a Roleblocker-type role to weaken it in setups where the intention is that the Roleblocker not be able to tie down the same player indefinitely.