Describing a loan made to a borrower whose credit record is poor, so the lender charges a higher interest rate to cover the higher risk of not being paid back. The word is banking jargon and it names the borrower's grade, not the loan's quality: *prime* borrowers are the safe ones with good records, so *sub*prime means below that line. You will see it in front of nouns — subprime mortgage, subprime lending, subprime borrower — and as a noun for the whole market (losses in subprime). Everyone who knows this word knows it because of one event: the American subprime mortgage crisis of 2007-2008, when banks lent heavily to people who could not repay, bundled those loans into investments, and set off a global financial crash. Because of that, *subprime* now carries a permanent whiff of recklessness and disaster in ordinary use — a journalist calling something 'the subprime of the education sector' means a bubble built on bad debt. Note it is a term of art, so it is never rude in banking, but a person would not call themselves a subprime borrower in conversation.