About NumberGlossary
A source-cited reference for the vocabulary of North American telephone numbering.
NumberGlossary defines the terms you need to read numbering data correctly — what an NPA is, how an overlay differs from a split, why the original assignee of a prefix is not the carrier serving a number today.
How it's made — honestly
These definitions are drafted with AI assistance from primary sources — the public records and technical documents of NANPA, the Canadian Numbering Administrator (CNAC), the FCC and the ITU — and every entry cites the sources it draws on. This is a bounded, controlled vocabulary: a fixed, reviewable set of real numbering terms, not an open-ended stream of auto-generated pages. We would rather define 25 terms carefully than publish thousands.
We do not claim these are hand-written by experts or that each has passed independent human review — they have not. What we do claim, and what we think actually matters, is that every statement is traceable to a cited source and open to correction. If you find an error, tell us at corrections@numberglossary.com and we will fix it and note the change.
Each entry carries its sources, a last-updated date, its relationship to other terms (broader, narrower, related), and the misconception people most often bring to it. Where a term describes something you can observe in real data, we link to a live example on NumberResearch.
What this is — and isn't
NumberGlossary answers "what does this term mean." It is the reference layer. For the current state of any specific area code, prefix or relief decision — the live numbers — see NumberResearch.org, which is built on the official NANPA, CNAC and FCC records.
We do not do reverse lookups, current-carrier identification, or "who is calling" — those require portability data and are outside a glossary's job. The number decoder explains a number's structure; it deliberately does not identify its owner.
Tools
- NANP number decoder — break a number into its parts, each explained and backed by live data. The number stays in your browser.
- Commonly confused terms — the pairs people mix up, side by side, with the tell that separates them.
Who publishes this
NumberGlossary.com is published by GreatNumber LLC as part of a network of North American numbering references. Corrections and questions: corrections@numberglossary.com.
Definitions are licensed CC BY 4.0 — attribute NumberGlossary.com. Underlying facts originate from NANPA, CNAC, the FCC and the ITU.