Nirmāṇakāya is a Sanskrit term in Mahāyāna and Vajrayāna Buddhism that refers to the “emanation body” or “manifestation body” of बुद्ध a Buddha. It is one of The Three Kāyas that comprise the त्रिकाय Trikāya (The Three Bodies) doctrine of बुद्धत्व Buddhahood, along with the Saṃbhogakāya (bliss body) and धर्मकाय Dharmakaya (truth body).
The Nirmāṇakāya is the form that a Buddha takes to manifest in the physical world to guide and teach sentient beings. It is through this body that Buddhas can appear in any form necessary, whether as human, animal, or other beings, to best suit the needs of those they are helping on the path to enlightenment. The most famous example of a Nirmāṇakāya is the historical Buddha, Siddhartha Gautama, who manifested in human form to teach the धर्म Dharma and lead others toward liberation.
In contrast to the transcendental and eternal nature of the धर्मकाय Dharmakaya, which represents the Buddha’s ultimate, formless reality, the Nirmāṇakāya operates within the relative world of form and duality. It is through the Nirmāṇakāya that the teachings are made accessible to beings who are still enmeshed in the cycle of birth, death, and suffering (संसार Saṃsāra).
While the Nirmāṇakāya is a visible and tangible manifestation, it is still an expression of the Buddha’s awakened wisdom and compassion. It serves the purpose of helping others, embodying the Buddhist ideal of skillful means (upāya), where a Buddha or बोधिसत्त्व Bodhisattva can manifest in ways that are most effective for relieving suffering and imparting the Dharma.