Definition
REG is a legal abbreviation with several distinct historical and modern meanings, depending on the word or phrase it contracts.
1. REG. GEN. — Short for *Regula Generalis* (Latin: general rule). A general rule of court, as distinguished from a rule made in a specific case or on a particular motion.
2. REG. JUD. — Short for *Registrum Judiciale*. The register of judicial writs; a collection of standardized writ forms used in the common law courts.
3. REG. LIB. — Short for *Registrarii Liber* (Latin: the registrar's book). The register's book in Chancery, which contained all decrees issued by that court.
4. REG. ORIG. — Short for *Registrum Originale*. The register of original writs — the foundational catalog of writ forms from which common law actions were derived. Also called the *Registrum Omnium Brevium* or, in Chancery usage, the *Registrum Cancellaria*.
5. REG. PL. — Short for *Regula Placitandi*. A rule of pleading.
6. Modern regulatory usage — In contemporary legal and business contexts, REG (or Reg) functions as a shorthand prefix for named federal regulations, most prominently in securities law: *Reg NMS* (Regulation National Market System), *Reg FD* (Regulation Fair Disclosure), *Reg D* (Regulation D), *Reg S-K*, and others. This usage does not appear in the historical law dictionaries but dominates current practice.
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Common Language
Wiktionary: A diminutive of the male given name Reginald.
The gap between ordinary and legal usage here is total. In common speech, *reg* functions either as a nickname or, informally, as a shortening of "regulation" (as in "rules and regs"). In legal and regulatory contexts, the latter informal meaning has been formalized and capitalized — *Reg* as a named shorthand for specific regulatory regimes carries precise technical meaning that the ordinary colloquial sense does not approach.
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Common Confusion
Researchers encountering *Reg.* in older English legal sources must read carefully for context. The same three-letter abbreviation resolves to at least five distinct Latin phrases — *Regula Generalis*, *Registrum Judiciale*, *Registrum Originale*, *Registrarii Liber*, and *Regula Placitandi* — and the distinguishing qualifier (Gen., Jud., Lib., Orig., Pl.) may be absent, dropped, or obscured in transcription. Conflating the register of original writs with the register of judicial writs, for instance, produces a substantive research error: the first concerns the origination of actions; the second concerns writs issued in the course of pending litigation.
Modern researchers should also be alert to the complete shift in dominant meaning: in post-20th-century American legal sources, *Reg* almost always signals a named federal regulation, not a Latin abbreviation from the common law writ system.
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Why It Matters in Research
The primary research trap with REG is disambiguation across time and subject matter. Historical English legal materials — Year Books, chancery records, treatises — use Reg. as shorthand for Latin writ-register and court-rule terminology. The *Registrum Originale* in particular was a constitutive document of the common law: as Blackstone noted (3 Bl. Com. 183, cited in Burrill), it was "that most ancient and highly venerable collection of legal forms" from which suable writ forms were drawn. Understanding this abbreviation is foundational to reading older procedural and jurisdictional texts accurately.
In the Law Mind corpus, researchers moving from historical common law materials into modern corporate and securities law will encounter a complete vocabulary shift. The *Reg* prefix in securities regulation (Reg NMS, Reg FD, Reg D) refers to SEC rulemaking under the Securities Exchange Act of 1934 and related statutes — a body of law with no structural connection to the Latin abbreviations in the historical dictionaries. Cross-corpus searches using "Reg" as a keyword will surface both registers unless the researcher bounds the query by date, subject matter, or source type.
The Burrill entry is particularly valuable for its quotation from Blackstone regarding the *Registrum Originale*, offering a direct link between the abbreviation and the jurisprudential significance of the register system in pre-reform common law procedure.
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Historical Dictionary Support
Black's (1st and 2nd editions) and Burrill agree on the core set of Latin expansions and are consistent with each other. The 2nd edition of Black's reproduces the same sub-entries with minor typographic variation, suggesting no substantive doctrinal evolution between editions on this term. Burrill adds value by quoting Blackstone on the *Registrum Originale* and gesturing toward the broader register system, including the *Registrum Cancellaria* equivalence.
What the historical dictionaries do not address — and could not — is the modern Reg-prefix convention in American administrative and securities law. That usage postdates all three source dictionaries by decades and has effectively displaced the Latin abbreviation system as the primary legal meaning of the term in contemporary practice.
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Encyclopedia Cross-Reference
Law Mind Business Organizations & Corporate Law Encyclopedia — Special Topics: Market Regulation (Stock Exchanges, ECNs, and Reg NMS)
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