Yajna

In Hinduism, yajna (Sanskrit यज्ञ wikt:yajna; yagam (Tamil யாகம்) ;also Anglicized as Yajna, Yadna) is a ritual of sacrifice (also "worship, prayer, praise, offering and oblation, sacrifice" according to Monier-Williams) derived from the practice in Vedic times. Yajna is a ritual of sacrificing and sublimating the havana sámagri (herbal preparations) in the fire accompanied by the chanting of the Vedic mantras. The sublime meaning of the word yajna is derived from the Sanskrit verb yaj, which has a three-fold meaning of worship of deities (devapujana), unity (saògatikaraña) and charity (dána). An essential element is the sacrificial fire - the divine Agni - into which oblations are poured, as everything that is offered into the fire is believed to reach God. As the name of the service, the term yajna is linguistically (but not functionally) cognate with Zoroastrian (Ahura) Yasna. Unlike Vedic Yajna, Zoroastrian Yasna has "to do with water rather than fire".(Drower, 1944:78; Boyce, 1975:147-191)

Rituals associated with temple worship in Hinduism are called agamic, while those involving communication with divinity through Agni are considered to be Vedic. Temple rites in modern-day Hinduism are a combination of both Vedic and agamic rituals. The ritualistic portion of the Hindu scriptures is called Karma-Kanda. Parts of Vedas which describe or discuss Yajnas or sacrifices fall into this portion. The Nambudiri Brahmins of Kerala are among the most famous Śrauta Brahmins who maintain these ancient rituals.

Today, only a few hundred individuals know how to perform these sacrifices and even fewer are able to maintain the sacred fires continuously and perform the Śrauta rituals. Only a few thousand perform the Agnihotra or basic Aupasana fire sacrifice daily .

Read more about Yajna:  Rituals, Types of Yajnas, Types of Agni (Fire), Pancha Mahayajnas, Other Yajnas, Vows