Yagnas may include the sacrifice of ego, devotional worship, and oblations offered in reverence to the sacred power of God. 

 

It refers to an ancient ritual done in front of a blessed fire.  Special mantras are chanted and wood, fruits, oils, grains, honey, yogurt, and ghee (clarified butter) are poured into the sacrificial fire.  This is to honor and respect the divine powers of the universe and an Offering to the Lord.