Brahman is the ultimate reality, the source of all existence, and the goal of all spiritual seeking in the Upanishads.

The Upanishads teach that Brahman and Atman are one and the same, and that the realization of this unity is the ultimate goal of spiritual practice.

The Brihadaranyaka Upanishad is considered to be the oldest and most important Upanishad, and it contains some of the most profound and influential teachings on Brahman, Atman, and the nature of reality.

Maya refers to the illusion or veil that conceals the true nature of reality and prevents us from realizing our unity with Brahman.

The Mandukya Upanishad is known for its teachings on the four states of consciousness: waking, dreaming, deep sleep, and the fourth state, which is beyond the other three.

The ultimate goal of spiritual practice according to the Upanishads is to attain moksha, which is liberation from the cycle of birth, death, and rebirth and the realization of one's true nature as Brahman.

The Taittiriya Upanishad is known for its teachings on the five sheaths of the self, which are the physical body, the vital breath, the mind, the intellect, and the bliss sheath.

Om is considered to be the symbol of Brahman, the ultimate reality, and it is often used as a mantra in meditation and spiritual practices.

The Isha Upanishad is known for its teachings on the unity of all beings and the importance of living in harmony with the world.

The Brihadaranyaka Upanishad contains the famous line, 'Aham Brahmasmi' (I am Brahman), which expresses the realization of the unity of the individual self with the universal Self.

The Katha Upanishad is known for its teachings on the nature of time, including the idea that time is cyclical and that the universe undergoes periods of creation and dissolution.

The Katha Upanishad contains the story of Nachiketa and Yama, the god of death, in which Nachiketa seeks knowledge about the nature of death and the afterlife.

The Brihadaranyaka Upanishad is known for its teachings on the importance of self-knowledge, including the idea that true knowledge is the knowledge of the Self.

The Brihadaranyaka Upanishad contains the famous line, 'Neti, neti' (Not this, not this), which is used to describe the ineffable nature of Brahman.

The Brihadaranyaka Upanishad is known for its teachings on the relationship between the individual self and the cosmic Self, including the idea that the individual self is a spark of the cosmic Self.