What is exactly is need based aid?

there are different kinds of need-based aid and a school can offer you several of them in the same financial aid package.

1) grants - these are free money (basically scholarships) that you do not need to pay back. anything called an "grant" falls under that category

2) need-based loans - these are usually federal subsidized or unsubsidized loans, and you do need to pay these back. subsidized loans cover your interest while you're in college, while unsubsidized loans do not. they both have relatively low interest rates that are set by congress, so anyone can take them out

3) work-study - basically, you get a campus job that's partially paid by the school and partially paid by a government program (this makes it easier to get that job in the first place). you earn money as you would for any job, but you're expected to pay that towards tuition.

most schools will offer a certain amount of loans first (those federal loans are capped at around $5500 for freshmen), then work-study, then grant aid to make up the difference between their cost and a family's EFC. some schools—mainly Ivies (excluding Cornell)—guarantee to only offer grant aid/work-study and no loans, so all of their aid is free money that you don't have to pay back.

Need based aid is a type of scholarship/grant that you qualify for depending on how much you need it (e.g. if your household income is quite low you may qualify for aid). You do not have to pay these back because they are need based. However, if it were a self-help aid, you would have to pay that back because it is a loan.