In the simplest case, payoff means a reward or reinforcement that
the system gets from the environment. It's a scalar quantity, like 37
or 764.3. An individual classifier's payoff prediction is its
estimate of what the system will get if the system takes the action
recommended by this classifier.
In the general case, payoff may also be an estimate of a combination of
external (from the environment) reward, and various forms of internal
reward that the system employs in its operation.
What do you mean by "payoff"?