ISO6392T

ISO 639-2/T refers to the terminological set of three-letter language codes defined within ISO 639-2, the international standard for language identifiers. The ISO 639-2 framework provides two independent code sets for some languages: a bibliographic code (B) and a terminological code (T). The T set is intended to be used in terminological, technical, and standardized contexts, and it often reflects native names or conventional terminology. While many languages share identical B and T codes, notable differences exist for several languages to better align with native usage or terminology.

Notable examples of differing B and T codes include Greek, Romanian, and Persian. The bibliographic Greek code is gre, whereas the terminological code is ell. Romanian is rum in the bibliographic set and ron in the terminological set. Persian uses per in the bibliographic set and fas in the terminological set. In many languages the two sets are identical, but the distinctions are important in certain catalogs, databases, and dictionaries to avoid ambiguity or to meet terminology conventions.

ISO 639-2/T is part of the broader ISO 639 language-coding family. It complements ISO 639-1 (two-letter codes) and ISO 639-3 (a later, more expansive three-letter code set that aims for comprehensive coverage and includes a single code per language). In practice, 639-2/B and 639-2/T codes continue to be used in libraries and metadata systems, while 639-3 provides broader linguistic coverage and modern terminology concepts.