In case you don’t remember, the housing crisis we’re finally getting out of was caused by, at its core, people getting mortgages they couldn’t afford. Blame the borrowers, blame the lenders, whatever — that was the root of it all.
That was the sub-prime market: loans to people who didn’t have great (aka “prime”) credit. And that’s why we have all these new rules and regs and requirements: to prevent people — many of whom didn’t know any better — from borrowing more than they can afford. (Or at least shielding taxpayers from lenders willing to take the extra risk on those people.)