Yajna is from the SANSKRIT root yaj, “to honor a god with oblations.” A yajna is a ritual involving oblations in the Vedic tradition. It may be simply an offering of clarified butter into a fire, or it may involve 17 priests in an elaborate 12-day ritual including the building of a large fire altar as in the AGNICHAYANA. The ritual of the yajna always includes a fire, Sanskrit MANTRAS, and some sort of offering. In the larger public rituals a sacrifice of some animal or animals has been common. The word yajna is frequently translated roughly as “sacrifice.”
Further reading: Jan Gonda, Vedic Literature (Samhitas and Brahmanas): A History of Indian Literature, Vol. 1, no. 1 (Wiesbaden: Otto Harrassowitz, 1975); Thomas Hopkins, The Hindu Religious Tradition (Encino, Calif.: Dickenson, 1971); Frits Staal, AGNI: The Altar of Fire, 2 vols. (Berkeley, Calif.: Asian Humanities Press, 1983).
Encyclopedia of Hinduism. A. Jones and James D. Ryan. 2007.