Nonduality is the state of being intimately connected to everything, feeling a sense of oneness with the entire universe. In this experience, the distinction between the observer and the observed disappears, and the individual feels as one with what they are observing. For example, one does not see a mountain, they become the mountain. This experience also eliminates the distinction between the thing being observed and the observer, they are seen as empty but vivid experiences. Nonduality is the state of pure experience without division between subject and object, observer and observed.
Different cultures have developed various techniques to help individuals experience nonduality, but it can also be an innate human experience. It is possible to induce it through meditation practices, but it can also be revealed through pointing it out. Nonduality is at the core of human experience and is present in most religions and philosophies, with particular emphasis in Hinduism and Buddhism.
Nonduality is considered to be the essence of spiritual awakening, encompassing enlightenment, liberation, realization, and divine union. The process of awakening through nonduality can take a lifetime and constantly deepens and broadens to encompass more areas of one’s life.

Adi Shankara is credited with organizing the principles of Advaitic theosophy in the 8th century AD. It is a fusion of traditional Vedanta scripture and Buddhism.
The writings of more recent sages such as Atmananda Krishna Menon, Nisargadatta Maharaj, and Ramana Maharshi as well as contemporary teachers such as Francis Lucille, Rupert Spira and Adyashanti provide deeper insights into Nonduality. 

It is an experience of pure being, without cognition, in which all separation ceases. It is an awakening from all fixed points of view and the end of all division. It is the realization that there is just one self, without a difference or gap between the revelation of oneness and the way it is perceived and lived every moment of life. It is the state of consciousness, our true nature, which reveals itself as absolute happiness, love, and beauty.