A holocaust is a religious animal sacrifice that is completely consumed by fire. The word derives from the Ancient Greek holocaustos (ὁλόκαυστος = ὁλον [wholely] + καυστος burnt), which is used solely for one of the major forms of sacrifice. When the Tanakh was translated into Greek, the translators used the term for a similar ritual among the Jews.
These are the two ideal types of Greek sacrificial ritual; they are appropriate to different divinities, done for different purposes, and conducted by different methods. Holocausts are apotropaic rituals, intended to appease the spirits of the Underworld, including the Greek heroes, who are spirits of the deads; they are also given to malign powers, such as the Keres and Hecate. One of the earliest attested holocausts was Xenophon's offering of pigs to Zeus Meilichius.
Holocausts are conducted at night, without wine, and offer black-hided animals at a low altar, with their heads directed downwards; in all these they are opposed to the commensal sacrifice given to the Olympian gods. (This distinction is between extreme types, and was somewhat exaggerated in the early twentieth century, as by Jane Harrison; considerable evidence has been also been found of commensal sacrifice offered to heroes.)
Whole offerings were also made as sin offerings on the appointment of a priest, on the termination of a Nazirite's vow, after recovery from Tzaraas (often translated leprosy, following the Septuagint's translation as lepra), shortly after childbirth, after Niddah (menstruation) or recovery from zivah (abnormal bodily discharges), or as a voluntary sacrifice, when the sacrificial animal could be a young bull, ram, year-old goat, turtle doves, or pigeons.
The whole offering is believed to have evolved as an extreme form of the slaughter offering, whereby the portion allocated to the deity increased to all of it. In slaughter offerings, the portion allocated to the deity was mainly the fat, the part which can most easily be burnt (fat is quite combustible); scholars believe it was felt that the deity, being aethereal, would appreciate aethereal food more than solid food—the burning of the fatty parts of animals being to produce smoke as a sweet savour for the deity. Some passages in the Book of Judges, dated by textual scholars to periods earlier than the Priestly Code, appear to show the development of the principle and practise of whole offerings; in the story of Gideon, a slaughter offering of a young goat and unleavened bread is destroyed when fire sent from heaven consumes it; in the story of Samson's birth, his father, who was intending to make a slaughter offering so that he could give a meal to an angel, is told by the angel to burn it completely instead.
Most biblical scholars now agree that the intricate details of the whole offering, particularly the types and number of animals on occasion of various feast days, given by the Torah, were of a late origin, as were the intricate directions given in the Talmud. Whole offerings were quite rare in early times, but as the ritual became more fixed and statutory, and the concentration of sacrifice into a single sanctuary (particularly after Josiah's reform) made sacrifices quite distinct from simply killing animals for food, whole offerings gradually rose to great prominence.
Some of the Jewish sacrifices specified by the Torah, the olah was completely burnt. These, whole offerings, were referred to in Hebrew as `olah, a term translated as holocauston in the Septuagint. Today, some English Bible translations render the word as holocaust, and others translate it as burnt offering. For example, Exodus 18:12a is translated in the New American Bible as Then Jethro, the father-in-law of Moses, brought a holocaust and other sacrifices to God, while it is translated in the New International Version as Then Jethro, Moses' father-in-law, brought a burnt offering and other sacrifices to God.
In the mid-nineteenth century the word began to be used by a large variety of authors to reference large catastrophes and massacre. In the 20th century it became strongly associated with the Final Solution of the Nazis' Third Reich.