In money terms, the idea is that someone loans an amount of money to someone or a project and that person or project “pays back” the loan by giving the money to someone or something else.
So as far as this campaign is concerned; I’m hoping that you will help fund my project by “lending” me the money to buy a Race Chair. In turn, I will “pay back” your loan by giving that amount of money to someone else with a similar dream. The chair you help me fund will be used to generate income via sponsored events. That’s how I’ll “pay your loan forward” to someone else. Get it?
For more, see Wikipedia: