A reinforcer is something that encourages or rewards a behavior, making it more likely to happen again in the future. It can be a tangible item, an activity, or even just praise or recognition.
The use of reinforcers amounts to a promise that if the dog will behave in the way you desire, you will reward him for that behavior. (midatlanticbullybuddies.org)
It is reinforcing because it is paired with the Primary Reinforcer of PLAY». (boogiebt.com)
Therefore, we can not say that all dogs need to be trained with a particular type of food, or that having tugs of war with the dog will work as reinforcers in each case. (animalwised.com)