A reinforcement schedule is the pattern of reward that is used in behavioral theory. This can be anywhere between rewarding every correct behavior (continuous reinforcement) to intermittent reinforcement (giving rewards occasionally for the desired behavior.
For instance, when training a puppy to sit using a continuous reinforcement schedule you would reward it every time it sits on command. On the other hand if you used an intermittent reinforcement schedule you would only reinforce the puppy every other time they sit or after a random number of times. Intermittent reinforcement schedules are a much more powerful reinforcement schedule because the behaviors last longer and are more resistant to extinction. Intermittent reinforcement schedules are the driving force behind gambling. Lotteries and casinos let patrons win just often enough to keep them playing.