An initial public offering (IPO) refers to the process of a private company going public and selling its shares to the general public. The aftermarket, also known as the secondary market, is where these shares are traded after the IPO. If the stock price of an IPO falls below its initial issue price in the aftermarket, it is considered to be trading at a discount. This can happen due to various factors such as market conditions, company performance, and investor sentiment. As a knowledgeable finance professor, it is important to understand these terms and their implications in the stock market.