The Mahavakyas (sing.: mahāvākyam, महावाक्यम्; plural: mahāvākyāni, महावाक्यानि) are “The Great Sayings” of the Upanishads, as characterized by the Advaita school of Vedanta. Most commonly, Mahavakyas are considered four in number,^[1][2]
Prajñānam Brahma (प्रज्ञानम् ब्रह्म) – “Insight is Brahman,” or “Brahman is insight”^{[web 1]} (Aitareya Upanishad 3.3 of the Rig Veda)
Ayam Ātmā Brahma (अयम् आत्मा ब्रह्म) – “This Self (Atman) is Brahman” (Mandukya Upanishad 1.2 of the Atharva Veda)
Tat Tvam Asi (तत् त्वम् असि) – “That essence (tat, referring to sat, “the Existent”^[3][4]) are you” (Chandogya Upanishad 6.8.7 of the Sama Veda)
Aham Brahmāsmi (अहम् ब्रह्मास्मि) – “I am Brahman” (Brihadaranyaka Upanishad 1.4.10 of the Yajur Veda)
They all express the insight that the individual self (jiva) which appears as a separate existence, is in essence (atman) part and manifestation of the whole (Brahman).