1 According to Sāṃkhya-Yoga ontology, the female of the two fundamental principles (the other being the male, puruṣa) which constitute reality. Invisible and unconscious, prakṛti in its unmanifest form (also known as pradhāna) is the ultimate cause of all material existence. The evolution of the universe occurs when the perfect equilibrium of the three guṇas, which are synonymous with the unmanifest prakṛti, is disturbed by the proximity of puruṣa. This results in prakṛti manifesting itself in the form of evolutes, which develop to constitute the material universe and all that it contains, including the physical and mental attributes of human beings—the 25 tattvas of classical Sāṃkhya. At the cosmological level, the process is never-ending: the tattvas will be reabsorbed into unmanifest prakṛti, only to evolve again in a continuous cycle. For the individual, bondage is the delusion that it is the inherently passive puruṣa which is acting and experiencing the results of action (karma), when in fact, it is prakṛti, through the guṇas, which is the sole cause of action. In a theistic modification of this (in, for example, the Bhagavadgītā), prakṛti and its evolutes are said to comprise God's lower nature, while sentient beings (puruṣas) constitute his higher nature. An even more radical redefinition occurs in Śākta traditions, where śakti, the Goddess, and prakṛti are considered to be identical, a single active consciousness, in which puruṣa is subsumed.
2 In Vedic śrauta ritual, a basic paradigm or model (prakṛti) which is modified to produce a series of more complicated sacrifices. Three types of sacrifice are considered to be prakṛtis in this sense: the darśapūrṇamāsa, the paśubandha, and the agniṣṭoma.