Under current U.S. Regulation NMS, a “bid or offer” is the bid price or offer price communicated by an exchange or association member to a broker, dealer, or customer at which it is willing to buy or sell one or more round lots of an NMS security as principal or agent; indications of interest are excluded. Keep this definition tied to 17 CFR § 242.600; everyday uses of bid and offer and other market-rule definitions can differ.
Under current U.S. Regulation NMS definitions, best bid and best offer mean the highest-priced bid and the lowest-priced offer. Treat this as a U.S. securities-regulation definition. Do not collapse it into the NBBO concept or generalize it to every use of best price outside this rule context.
The National Best Bid and Offer (NBBO) is the U.S. national-market benchmark formed from the highest displayed bid and the lowest displayed offer used in the applicable NMS framework. NBBO is a U.S. market-structure term and should not be generalized into a universal global best-price concept or confused with one venue’s local best bid and offer.
Under current U.S. Regulation NMS definitions, published bid and published offer are the bid and offer quotations of a national securities exchange or national securities association that are communicated to a securities information processor. The rule defines the bid and offer jointly. Keep them in one canonical and do not split them into competing standalone pages.
A bid-ask spread is the gap between quoted buying and selling prices and is one market-liquidity measure; wider spreads generally imply greater trading cost or compensation for liquidity provision. Treat the spread as one dimension of liquidity, not as a complete measure of market liquidity, depth, or price impact.
Midpoint-or-Better Limit Order is a current Regulation NMS defined term. This guide keeps the non-marketable requirement, side-specific midpoint test, and determination-time conditions together.
Registered Broker or Dealer Under Regulation AC is a current Regulation AC defined term. This guide preserves the rule-specific meaning and boundary instead of replacing it with informal market shorthand.
“Responsible broker or dealer” is a defined Regulation NMS role linked to responsibility for communicating quotations in the rule’s exchange or association contexts. It is not a generic label for whichever broker happens to handle an order.
