A "notice of default" is a formal notification sent to a borrower when they fail to make required payments on a loan, typically a mortgage. This document serves as a warning that the lender, such as a bank or financial institution, may initiate foreclosure proceedings if the borrower does not rectify the missed payments. The notice outlines the amount owed and provides a specific timeframe for the borrower to respond or make payments. If the borrower does not take action, the lender may proceed with legal steps to reclaim the property, which is often referred to as foreclosure.