Yajna (यज्ञः)
All activities in the limitless expansion of the universe are said to have generated from a grand eternal Yajna(Yagya). Atharva Veda (9.15.14) describes Yagya as: Ayam Yajna Vishvasya Bhuvanasya Nabheehiâimplying Yagya as the fundamental process of manifestation of nature.
In physical terms, Yagya (homam, havan or agnihotra) is a process of herbal sacrifices in holy fire aimed at the finest utilization of the subtle properties of sacrificed matter with the help of the thermal energy of fire and the sound energy of the mantras. Modern scientific research has also shown significant therapeutic applications of Yagya and also affirmed its potential in purification of environment.
Literally speaking, Yagya means - selfless sacrifice for noble purposes. Sacrificing ego, selfishness and material attachments and adopting rational thinking, humane compassion and dedicated creativity for the welfare of all - is indeed the best Yagya which should be performed by all human beings. The philosophy of Yagya teaches a way of living in the society in harmony, a living style to promote and protect higher humane values in the society - which is indeed the basis of the ideal human culture.
http://www.awgp.org/spiritual_wisdom/yagya
Vedic yagyas (other name yajna, yagna) are performed to create positive effects and avoid unwanted effects in the different areas of life of individuals and nations and to have the best possible nature support. Many people use the yagna or yajna words instead of yagya, the meaning of it is the same. We use the vedic word because yagyas are based on the knowledge of the ancient saints of vedic tradition. Vedic yagyas are done by specially trained vedic pandits (pundits), who are the experts of vedic ceremonies, performances, and who live their lives' according to the rules of vedic tradition. Yagnas, yajnas are performed through the recitation of sound or vedic mantras to reach certain of result. This is vedic music, vedic vibration. It is possible to use them as prevention but it is also possible to use them for promoting the different areas of life. The benefits of the yagya rigning are the vedic health, wealth, harmony and evolution. Our head pandit is the expert of jyotish, that vedic science which can be used to predict the life events of the individuals and which can be the well-grounded base of suggesting the necessary yagya services for a balanced life.