According to the GDPR, what is a description of binding corporate rules (BCR)?

According to Article 4(20) of the GDPR, Binding Corporate Rules (BCRs) are defined as "personal data protection policies which are adhered to by a controller or processor... for transfers... of personal data to a controller or processor in one or more third countries within a group of undertakings, or group of enterprises engaged in a joint economic activity." They are essentially a corporate code of conduct or internal rulebook that allows multinational companies to transfer personal data from their EEA-based entities to their non-EEA entities while providing adequate safeguards for the data. These rules must be approved by a competent data protection authority as per the consistency mechanism outlined in Article 47.

A. This describes an adequacy decision, which is a finding by the European Commission under Article 45 of the GDPR, not Binding Corporate Rules.
C. This describes the function of any appropriate safeguard under Article 46 of the GDPR (like Standard Contractual Clauses), but it is not the definition of what BCRs are.
D. BCRs under the GDPR specifically legitimize transfers from the EEA to non-EEA countries within a group, not transfers exclusively between non-EEA countries.

1. General Data Protection Regulation (EU) 2016/679:

Article 4(20): Provides the official definition of 'binding corporate rules'.

Article 47(1): States that a competent supervisory authority shall approve binding corporate rules provided that they are legally binding, applied by every member of the group, and confer enforceable rights on data subjects.

2. European Data Protection Board (EDPB) / Article 29 Working Party (WP29):

Working Paper WP259 rev.01, "Working Document setting up a table with the elements and principles to be found in Binding Corporate Rules," adopted on 11 April 2018. Section 1, Introduction, describes BCRs as "internal rules (such as a Code of Conduct) adopted by a multinational group of companies... which define its global policy with regard to the international transfers of personal data from a group’s entity located in the EEA to a group’s entities located in other parts of the world."