An XBRL taxonomy is the standardized dictionary of reporting concepts that XBRL tags refer to. It defines each reportable element — "Revenues," "Net Income (Loss)," "Total Assets" — along with its precise meaning, data type, valid relationships, labels, and references to accounting standards. Tagging a number in a filing means linking it to a specific taxonomy element.
The most widely used taxonomy for U.S. public-company financial statements is the U.S. GAAP Financial Reporting Taxonomy, maintained by the FASB and approved annually by the SEC.
Full guide: What Is XBRL? How SEC Tagging Affects Your Investment Data (2026)
A taxonomy organizes concepts into structured relationships using linkbases that describe how elements relate — how line items roll up into subtotals (calculation), the order they are presented in (presentation), and what labels and references apply. When a company needs to report something the base taxonomy does not contain, it can create an "extension," adding a custom element while still anchoring to the standard. That anchoring is why the same financial concept can be located across thousands of filers. For the broader picture of how XBRL works, see the guide linked below.
A: The FASB develops and maintains the U.S. GAAP Financial Reporting Taxonomy, and it is reviewed and approved annually by the SEC for use in EDGAR filings. It is updated each year to reflect new accounting standards and reporting practices.
A: An extension taxonomy is a set of custom elements a company adds when the standard taxonomy does not contain a concept it needs to report. Extensions let filers tag company-specific line items while remaining compatible with the base U.S. GAAP taxonomy.
A: Linkbases are the files in a taxonomy that define relationships between elements — including how line items calculate into totals, how they are presented, and what labels and references apply to each concept.
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