Debt issued via public offering or public placement (Rule 144A) that is rated below investment grade by S&P or Moody's. This means that the debt is rated below the top four rating categories (i.e. S&P BB+, Moody's Ba2 or below). The lower rating is indicative of higher risk of default, and therefore the debt carries a higher coupon or yield than investment grade debt. Also referred to as Junk bonds or Sub-investment grade debt.