High yield debt (non-investment grade or junk bond) is a business term referring to a corporate debt instrument, usually a bond, that has a higher yield (compared to investment grade debt) because of a high perceived credit risk (default risk).
In modern economies, debt is bought and sold in the form of bonds traded in organized markets. The price of a bond is determined by numerous factors, including the interest rate, the term (amount of time before the bond is paid back in full, also known as the time to maturity) and the degree of risk associated with the underlying assets.