Prajñaparamita and the Heart Sutra
"Emptiness is not a blank state. As Avalokiteshvara said, 'Emptiness is form,' so it is not just a blank, dark state. It contains the fullness of all qualities. For example, if a rainbow appears, and you run after it in hopes of catching it, will you be able to catch the rainbow? Of course not, and yet there is a rainbow.
What is the nature of Prajnaparamita? It is the wisdom that realizes directly phenomena as they are: a wisdom free from extremes, having gone to, or in the process of going to, the "other shore,” beyond all abiding in any particular position. The Sanskrit term Prajnaparamita is translated many ways: for example, "supreme transcendent wisdom,” "the great emptiness,” "the true nature of all phenomena,” or "the absolute truth.” All these names refer to the ultimate level of every teaching given by Buddha Shakyamuni. It is the profound essence of the Mahayana, and in the Vajrayana it is the very basis of every practice. It is therefore important that we who have entered the path and begun Vajrayana training acquire some depth and subtlety in our understanding of Prajnaparamita."*
The Heart Sutra is part of a larger body of scripture called the Prajnaparamita, and was among the first of these teachings to be translated from Sanskrit into Tibetan. It is considered to contain in its few lines the essence, or condensed meaning, of the entire Prajnaparamita.
* from a commentary by the Ven. Khenchen Palden Sherab Rinpoche and translated by the Ven. Khenpo Tsewang Dongyal Rinpoche