What do Kickstarter backers get in return?

So, I'm curious, what exactly do the backers on Kickstarter receive in exchange for their financial support? Do they get a product, a service, or something else entirely? Is there a specific reward system in place that determines what backers get? And is there any way to know what the rewards will be before making a pledge? I'm really interested in understanding the incentives for backers and how they are rewarded for their contributions.