Advaita Vedanta (IAST Advaita Vedānta; Sanskrit: अद्वैत वेदान्त ) is a philosophical concept where followers seek liberation/release by recognizing identity of the Self (Atman) and the Whole (Brahman) through long preparation and training, usually under the guidance of a guru, that involves efforts such as knowledge of scriptures, renunciation of worldy activities, and inducement of direct identity experiences. Originating in India before 788 AD, Advaita Vedanta is widely considered the most influential and most dominant sub-school of the Vedānta (literally, end or the goal of the Vedas, Sanskrit) school of Hindu philosophy. Other major sub-schools of Vedānta are Viśishṭādvaita and Dvaita; while the minor ones include Suddhadvaita, Dvaitadvaita and Achintya Bhedabheda.
Advaita (literally, non-duality) is a system of thought where "Advaita" refers to the identity of the Self (Atman) and the Whole (Brahman). Recognition of this identity leads to liberation. Attaining this liberation takes a long preparation and training under the guidance of a guru.
The key source texts for all schools of Vedānta are the Prasthanatrayi—the canonical texts consisting of the Upanishads, the Bhagavad Gita and the Brahma Sutras. The first person to explicitly consolidate the principles of Advaita Vedanta was Shankara Bhagavadpada, while the first historical proponent was Gaudapada, the guru of Shankara's guru Govinda Bhagavatpada.
Read more about Advaita Vedanta: History of Advaita Vedanta, Texts, Philosophy, Status of Ethics, Advaita and Other Indian Philosophies, List of Teachers