Definition & Terms Day Trading - The purchase and sale of the same stock symbol on the same day. Day Trader -  An active stock intra-day trader, who generally holds positions for a very short time and makes several trades each day. Day traders are individuals who are trying to buy and sell stocks quickly, often making dozens of trades in a single day and usually closing all positions at the end of each day. NASD - National Association of Securities Dealers. A self­regulatory securities industry organization responsible for the operation and regulation of the Nasdaq stock market and over-the-counter (OTC) markets. The NASD investigates complaints against member firms and tries to ensure that all of its members adhere to both its own standards and those laid out by the SEC. The NASD has the power to expel its members from an exchange, but it cannot take legal action against a member other than by reporting it to the SEC. The association is run by a board that takes half of its representatives from the securities industry and half from the public. SEC - Securities and Exchange Commission. The primary federal regulatory agency for the securities industry, whose responsibility is to promote full disclosure and to protect investors against fraudulent and manipulative practices in the securities markets. The Securities and Exchange Commission (SEC) enforces, among other acts, the Securities Exchange Act of 1933, the Securities Exchange Act of 1934 and the Investment Company Act of 1940. The supervision of broker-dealers is delegated to the self-regulatory bodies of the exchanges. like the NASD. It has five commissioners, each appointed for a five year term that is staggered so that one new commissioner is being replaced every year. The Securities and Exchange Commission is comprised of four basic divisions: The Division of Corporate Finance, the Division of Market Regulation, the Division of Investment Management and the Division of Enforcement.