Reinforcement learning

The last type of learning in machine learning is reinforcement learning, in which there's no supervisor but only a reward signal.

So the reinforcement learning algorithm will try to make a decision and then a reward signal will be there to tell whether this decision is right or wrong. Also, this supervision feedback or reward signal may not come instantaneously but get delayed for a few steps. For example, the algorithm will take a decision now, but only after many steps will the reward signal tell whether decision was good or bad.