NASD is the acronym of the National Association of Securities Dealers. It has been merged out of existence, but is a parent of the Nasdaq stock exchange and the Financial Industry Regulatory Authority.
The National Association of Securities Dealers was formed by the SEC in 1938 to regulate trading in the "over-the-counter" markets. The Maloney Act created the NASD to be a self-regulating body enforcing fair practices, thus increasing confidence in the markets. NASD remained under the auspices of the SEC, which had say-so over its decisions.
NASD was merged in 2007 with the enforcement arm of the New York Stock Exchange to become the Financial Industry Regulatory Authority, or FINRA. So NASD doesn't exist anymore. The regulatory authority looks out for individual investors by licensing and policing stock brokers.
Guess what? 'Nasdaq' is the acronym of the National Association of Securities Dealers Automated Quotations and is an American stock exchange which is the largest electronic screen-based equity securities trading market in the United States.
The Nasdaq is an over-the-counter market, or dealer market, which is different than a market in "over-the-counter" stocks, which do not meet the rules qualifying them to trade on the major exchanges. A dealer market in this case means that dealers -- so-called "market makers" -- are trading from their own stock accounts, using their own research and expertise. The dealers communicate by electronic means.