Foreclosure is the legal process a lender uses to take back a home when the borrower stops making mortgage payments. Because the house itself secures the loan — the lender holds a lien on it — the lender can force a sale to recover what's owed.
It doesn't happen overnight. Miss one payment and you're late; miss several and the lender issues a formal notice of default. From there, timelines vary by state, but the borrower typically has months to catch up, negotiate, or sell before the home goes to auction.
Why it matters even if you never miss a payment: foreclosure is the risk that shapes the whole mortgage system. It's why lenders scrutinize your debt-to-income ratio and why borrowing less than the maximum you're approved for is a genuinely defensive move.
If you're ever headed for trouble, act early — lenders would usually rather modify a loan, approve a repayment plan, or allow a short sale than foreclose. A foreclosure also drags down your credit score for years, so nearly any alternative beats riding it out.