Definitions
Rule 6621 is one of the shortest rules in the entire FINRA rulebook, consisting of a single operative sentence: terms used throughout the Rule 6620 Series carry the same meaning as those defined in Rule 6420. Despite its brevity, this cross-reference does significant structural work. It means the entire vocabulary governing OTC Equity Security transaction reporting, timely reporting standards, short sale indicators, and ATS exemptions is not restated anywhere in the Rule 6600 Series. Every operative term a firm needs to correctly apply Rules 6610, 6622, 6623, 6624, 6625, and 6630 sits instead in Rule 6420, a rule that also serves the substantive quoting and trading provisions of the Rule 6400 Series.
Rule 6621 was adopted in its current form as part of the 2008 Consolidated FINRA Rulebook initiative, under SR-FINRA-2008-021, effective December 15, 2008, per Regulatory Notice 08-57. No further amendment to Rule 6621 itself has occurred since adoption. Because the rule contains no substantive content of its own, amendments affecting the meaning of terms used throughout the Rule 6600 Series are made instead to Rule 6420, and this entry treats those Rule 6420 amendments as the operative history relevant to understanding Rule 6621's practical scope.
A dedicated search for third-party legal or compliance commentary on Rule 6621 specifically returned essentially nothing distinct from commentary on Rule 6420 itself. That absence is informative rather than a research gap. A pure cross-reference rule with no independent operative content does not generate independent case law, enforcement actions, or law firm client alerts. Any practitioner discussion of terms like "OTC Equity Security" or "OTC Market Maker" is filed under Rule 6420, not under Rule 6621, and firms researching this area should search accordingly.
What Rule 6621 Actually Incorporates
Rule 6420 defines the terms Rule 6621 imports into the Rule 6600 Series. "OTC Equity Security" means any equity security that is not an "NMS stock" as defined in Rule 600(b) of SEC Regulation NMS. The definition expressly excludes any Restricted Equity Security. This definition was itself amended in 2010, under SR-FINRA-2010-003, to delete an older, less precise formulation that defined the term by reference to securities not "qualifying for real-time trade reporting."
That older language was replaced with the current, cleaner cross-reference to the SEC's own NMS stock definition. FINRA simultaneously eliminated a separate defined term, "non-exchange-listed security," relocating that concept to Rule 6440 and the Three Quote Rule under NASD Rule 2320(f) instead. This 2010 change matters because it tied FINRA's definition to a standard the SEC itself maintains, reducing the risk of the two regulators' classifications drifting apart over time.
"Restricted Equity Security" means any equity security that meets the definition of "restricted security" contained in Securities Act Rule 144(a)(3). This definition matters directly to the Rule 6600 Series because Restricted Equity Securities traded under Securities Act Rule 144A are subject to a distinctive next-business-day reporting deadline found in Rule 6622. That deadline is separate from, and considerably longer than, the ordinary 10-second standard applied to OTC Equity Securities generally.
"Normal market hours" means 9:30 a.m. Eastern Time to 4:00 p.m. Eastern Time. This definition anchors nearly every timing distinction found in Rule 6622, including the separate treatment of transactions executed in the 8:00 a.m. to 9:30 a.m. pre-market window. It also underpins the distinct rules governing Restricted Equity Security transactions executed after 8:00 p.m.
Market Participant and Quotation Definitions
"OTC Market Maker" means a member of FINRA that holds itself out as a market maker by entering proprietary quotations or indications of interest for a particular OTC Equity Security in any inter-dealer quotation system. This includes any system the SEC has qualified under Section 17B of the Exchange Act. A member is an OTC Market Maker only in those specific OTC Equity Securities in which it actually displays market making interest through an inter-dealer quotation system, not across its entire trading book.
"Non-Market Maker" is defined by simple contrast: a member of FINRA that is not an OTC Market Maker with respect to a particular OTC Equity Security. This binary framing recurs throughout the Rule 6600 Series wherever obligations differ based on market maker status. A firm can hold both statuses simultaneously across different securities, since the classification attaches security by security rather than to the firm as a whole.
"Quotation" means any bid or offer at a specified price with respect to an OTC Equity Security. It also includes any indication of interest by a broker or dealer in receiving bids or offers from others for that security, and any indication that a broker or dealer wishes to advertise its general interest in buying or selling a particular non-exchange-listed security. "Quotation medium" means any inter-dealer quotation system, publication, electronic communications network, or other device that brokers or dealers use to make known their trading interest to others, including stated offers to buy or sell.
Facility-Specific Definitions
"OTC Reporting Facility" means the service FINRA provides to accommodate reporting for trades in OTC Equity Securities executed other than on or through an exchange. It also covers trades in Restricted Equity Securities effected under Securities Act Rule 144A, together with dissemination of last sale reports. The definition carries an operational caveat directly relevant to how the ORF functions in practice.
For OTC Equity Securities and Restricted Equity Securities that are not eligible for clearance and settlement through the National Securities Clearing Corporation, the ORF's trade comparison function will not be available. The facility will still support entry and dissemination of last sale data on those securities, however, even without the comparison function. "OTC Reporting Facility Participant" means any member of FINRA in good standing that uses the OTC Reporting Facility, the threshold status term used throughout the operative rules in this series.
Series 7 and SIE Relevance
The SIE does not test these definitions in any depth. It touches on OTC markets only at a conceptual level, distinguishing exchange-listed from over-the-counter trading generally.
Series 7 candidates should have a working understanding of what distinguishes an OTC Equity Security from an NMS stock, since this distinction underlies broader product knowledge about where and how different securities trade. Series 7 candidates are unlikely to be tested on the Restricted Equity Security definition specifically. A basic grasp of Rule 144A resale securities is still worth retaining, given how frequently the concept recurs across the broader FINRA rulebook.
Series 63 and Series 65 Relevance
Series 63 and Series 65 candidates do not need this rule's definitions at any operative level. These exams test state securities law, fiduciary obligations, and investment adviser regulation rather than the mechanics of FINRA's trade reporting facilities. Candidates preparing for either exam can set this rule aside entirely without exam-readiness risk.
Series 24 Relevance
Series 24 candidates should pay closer attention to this material, since a principal supervising OTC trading or market making activity must correctly classify securities and market participant status under these definitions. Getting the classification wrong directly affects whether the firm's Rule 6622 reporting obligations are triggered and applied correctly.
Series 24 candidates should also be able to explain why the 2010 change to the OTC Equity Security definition mattered from a supervisory standpoint. Tying the definition to the SEC's own NMS stock standard, rather than a FINRA-specific formulation, reduced the risk of a firm's internal security classification falling out of alignment with the regulator's own framework over time.
Series 57 Relevance
Series 57 candidates, given their direct involvement in trade execution and reporting, should know the OTC Market Maker definition precisely. The key point to retain is that market maker status attaches security by security rather than to the firm as a whole.
A trader who displays market making interest in one OTC Equity Security through an inter-dealer quotation system is an OTC Market Maker only in that security. The same trader remains a Non-Market Maker in every other OTC Equity Security the firm trades unless that same interest is separately displayed there too.
Relevance to Working Financial Services Professionals
For compliance officers building trade reporting supervisory procedures, Rule 6621's function as a pure cross-reference means definitional monitoring cannot be confined to the Rule 6600 Series alone. Any amendment FINRA makes to Rule 6420, including one as apparently technical as the 2010 change to the OTC Equity Security definition, automatically changes the scope of every rule in the Rule 6600 Series. That change occurs without a corresponding amendment ever touching Rule 6621 or the operative reporting rules themselves.
Firms tracking regulatory change through keyword or rule-number alerts limited to the Rule 6600 Series specifically risk missing amendments that alter their obligations. The substantive change occurs in Rule 6420, not in the rule a firm might assume to monitor. This has a direct practical consequence for market making desks and inter-dealer quotation system operators, since OTC Market Maker status shifts security by security rather than firm-wide.
A firm's compliance obligations tied to market maker status can therefore shift intraday as a trading desk begins or ceases displaying market making interest in a particular OTC Equity Security. Firms operating their own inter-dealer quotation systems should also track how the Rule 6420 definition of "quotation medium" interacts with separate obligations under Rule 6439. FINRA has periodically amended the requirements applicable to member-operated IDQSs that permit real-time quotation updates in OTC Equity Securities, and those amendments depend on accurately identifying which systems meet the Rule 6420 definitions in the first place.
