Definition - What does Yagna mean?
Yagna is a Hindu ritual that has been performed since ancient times in which Agni Deva, the fire god, acts as a medium between man and the gods. It is performed in front of a fire and Vedic mantras are chanted. Yagna is a Sanskrit word meaning "worship," "sacrifice" or "offering."
There are thought to be 1,008 types of yagna: the Bhagavad Gita mentions 12.
Yogapedia explains Yagna
Yagna is performed to invoke the gods for their blessings and to also obtain favors from them. They are performed by four types of priests, namely adhvaryu, hotra, udgatra and brahman. The adhvaryu's role is to take care of the physical aspects of yagna; hotra recites invocations; udgatra chants the yagna verses while focusing on the vital breath; and brahman, who is considered the chief priest, comtemplates upon the moon god.
Yagnas are performed at a yaga sala. The four entrances of a yaga sala represent the four Vedas. The agni, meaning "fire," is created in the designated sacrificial location. Ahuti, meaning, "oblation," is offered into the sacred fire.