The term National Best Bid refers to the highest available bid price, which is a consolidated value from all of the national stock exchanges. The National Best Bid is the maximum price buyers are willing to pay for a security such as a stock.
The National Best Bid, or NBB, is updated throughout the day. It provides investors with the highest available bid price for a specific security. This is the highest price that a dealer, or other prospective buyer, is willing to pay for a security.
The NBB is a consensus price, since the value is consolidated from all of the major exchanges as well as market makers. For example, the Consolidated Quotation System (CQS) provides an electronic service that provides the NBB information for stocks traded on the New York Stock Exchange, regional exchanges in the United States, as well as issues traded by the Financial Industry Regulatory Authority.
The Securities and Exchange Commission (SEC) requires brokers to guarantee customers this price. Unfortunately, enforcement of the SEC's Regulation NMS is problematic, since the volume and pace of trades today make it difficult to prove an investor actually received the highest available bid price on their trade.