Yajna

(“sacrifice”) A fire sacrifice, which was the
primary religious act in the earliest stratum of Indian religion. This cult of sacrifice is elaborated in the greatest detail in
the Brahmana literature, in which sacrifice is portrayed as the means by which
the universe came into being. The performance of sacrifice needed highly trained
priestly technicians (rtvij), who were differently responsible for chanting parts of
the Rg, Sama, and Yajur Vedas, as well as
building and maintaining the sacred fire
that was the heart of the sacrificial action.
This cult of sacrifice was essentially based
on burning things in this sacred fire, conceived as the god Agni, so that Agni could
convey the offerings to the other deities.
These rites were so elaborate and expensive that they eventually fell into disuse; by
the turn of the common era, there was
also considerable ambivalence about the
animal sacrifices that were originally an
important part of many of these sacrifices.
These ancient rites are rarely performed
today, but in the present context the word
yajna can be used for any rite involving
the sacred fire, particularly one carried out
by a brahmin for a patron.