Complex sentence: National Best Bid and Offer (NBBO) is a regulation by the United States Securities and Exchange Commission that requires brokers to execute customer trades at the best available ask price when buying securities, and the best available bid price when selling securities.
Split into simpler sentences: National Best Bid and Offer (NBBO) is a term used in United States Securities and Exchange Commission regulations. Brokers are required to execute customer trades at the best available ask price when buying securities, and the best available bid price when selling securities.