The word ‘apūrva’ is a technical term employed by the Pūrva-mīmāṁsā system of Hindu philosophy which advocates the performance of all the prescribed Vedic rituals as the only means of obtaining the summum bonum of life.
Vedic sacrifices are said to produce results such as attaining heaven. The doubt that naturally arises is: How can an act performed here and now produce a result much later and somewhere else? Does it not violate the law of cause and effect?
This objection is answered by the Pūrvamīmāṁsā system by formulating the theory of śakti (potential energy). Just as a seed possesses in it the imperceptible power with the help of which it can produce the sprout, so does the soul possess the power to manifest the results of Vedic rituals. These rituals, as soon as they are completed, generate in the soul that śakti or power. Since this power did not exist previously (a-pūrva = not existing previously) but is generated as a result of the rites, it is termed ‘apūrva.’ This apūrva gets exhausted after producing its results.
See also ADṚṢṬA and KARMA.