The term Navagraha denotes the nine celestial bodies which are central to astrological calculations (and beliefs) (and not the nine planets as it is frequently erroneously translated). The sun, the moon, mars, mercury, jupiter, venus, saturn and the two shadow planets Rahu and Ketu constitute the Navagrahas.
The nine "grahas" or planets in our horoscope control our karma, our desires and their outcomes. Each of these nine planets exerts an influence in our lives, which is called "dasa" and it can be known from one's horoscope. Navagraha Puja is undertaken to reduce the negative effects and improve the positive energies related to a person.