XBRL is the eXtensible Business Reporting Language. XBRL is an XML-based syntax for exchanging facts that carry their own context, and that are reported against taxonomies. Today, XBRL is mostly used for submitting financial reports to regulatory authorities.
XBRL is an XML-based standard developed and promoted by XBRL International Incorporated, a not-for-profit consortium of agencies and companies.
It extensively uses XML and related technologies such as XML Schema, XLink, XPath, XML namespaces in order to reduce the uncertainty around the transmission of financial information.
An XBRL taxonomy defines the list of items that can be reported, and their datatypes. Taxonomy linkbases provide additional information, such as the labels that should be displayed to users (label linkbase), references (reference linkbases), dimensions (definition linkbase), validation rules (calculation and formula linkbases).
An XBRL instance is a list of facts that conforms with one or more taxonomies.
XBRL is used most often in a use case of financial regulation. Financial reports are provided by regulated entities to a regulatory agency. These XBRL instances typically use a 'base taxonomy' that captures the concepts of an accounting framework, such as US GAAP or IFRS. In some regulatory reporting, companies also create extension taxonomies. These extension taxonomies provide additional accounting concepts that the company uses, but which are not provided in the base taxonomy.
Base taxonomies often contain thousands of concepts, and are maintained by the owners of the intellectual property of the framework they capture. In the case of US GAAP, this is the Financial Accounting Standards Board.