The National Best Bid and Offer (NBBO) is a set of regulations put in place by the Securities and Exchange Commission (SEC) to ensure that investors receive the best possible prices when buying or selling securities. The NBBO refers to the highest bid price for a security that is currently being offered by buyers and the lowest ask price for a security that is currently being offered by sellers.The NBBO is determined by looking at the best bid and ask prices from all of the exchanges and market makers that are trading a particular security. This ensures that investors receive the best possible prices, regardless of which exchange or market maker they choose to trade through.The NBBO is a critical part of the securities market, as it helps to ensure that investors are not overcharged for securities and that they are able to buy and sell securities at fair prices. The NBBO is also important for market makers, as it helps them to ensure that they are not offering prices that are significantly different from those offered by their competitors.For example, if the NBBO for a stock is $100 for the bid price and $101 for the ask price, it means that the highest bid price for the stock is $100 (which is the highest price that someone is willing to pay for the stock) and the lowest ask price is $101 (which is the lowest price someone is willing to sell the stock for).In summary, The National Best Bid and Offer (NBBO) is a set of regulations put in place by the SEC to ensure that investors receive the best possible prices when buying or selling securities. The NBBO refers to the highest bid price for a security that is currently being offered by buyers and the lowest ask price for a security that is currently being offered by sellers. It is determined by looking at the best bid and ask prices from all of the exchanges and market makers that are trading a particular security, ensuring that investors receive the best possible prices, regardless of which exchange or market maker they choose to trade through. The NBBO is a critical part of the securities market, as it helps to ensure that investors are not overcharged for securities and that they are able to buy and sell securities at fair prices.