The Yajurveda (, , from meaning "worship", and veda meaning "knowledge") is the Veda primarily of prose mantras for worship rituals. An ancient Vedic Sanskrit text, it is a compilation of ritual-offering formulas that were said by a priest while an individual performed ritual actions such as those before the yajna fire. Yajurveda is one of the four Vedas, and one of the scriptures of Hinduism. The exact century of Yajurveda's composition is unknown, and estimated by Witzel to be between 1200 and 800 BCE, contemporaneous with Samaveda and Atharvaveda. The Yajurveda is broadly grouped into two – the "black" or "dark" (Krishna) Yajurveda and the "white" or "bright" (Shukla) Yajurveda. The term "black" implies "the un-arranged, unclear, motley collection" of verses in Yajurveda, in contrast to the "white" which implies the "well arranged, clear" Yajurveda. The black Yajurveda has survived in four recensions, while two recensions of white Yajurveda have survived into the modern times. The earliest and most ancient layer of Yajurveda samhita includes about 1,875 verses, that are distinct yet borrow and build upon the foundation of verses in Rigveda. The middle layer includes the Satapatha Brahmana, one of the largest Brahmana texts in the Vedic collection. The youngest layer of Yajurveda text includes the largest collection of primary Upanishads, influential to various schools of Hindu philosophy. These include the Brihadaranyaka Upanishad, the Isha Upanishad, the Taittiriya Upanishad, the Katha Upanishad, the Shvetashvatara Upanishad and the Maitri Upanishad. Two of the oldest surviving manuscript copies of the Shukla Yajurveda sections have been discovered in Nepal and Western Tibet, and these are dated to the 12th-century CE. Etymology Yajurveda is a compound Sanskrit word, composed of ya jus (यजुस्) and Veda (वेद). Monier-Williams translates yajus as "religious reverence, veneration, worship, sacrifice, a sacrificial prayer, formula, particularly mantras uttered in a peculiar manner at a sacrifice". Veda means "knowledge". Johnson states yajus means "(mostly) prose formulae or mantras, contained in the Yajur Veda, which are muttered". Michael Witzel interprets Yajurveda to mean a "knowledge text of prose mantras" used in Vedic rituals. Ralph Griffith interprets the name to mean "knowledge of sacrifice or sacrificial texts and formulas". Carl Olson states that Yajurveda is a text of "mantras (sacred formulas) that are repeated and used in rituals". Dating and historical context The core text of the Yajurveda falls within the classical Mantra period of Vedic Sanskrit at the end of