In the Upanishads, 'Brahman' is the fundamental principle of the universe, representing the ultimate reality or universal consciousness from which all existence originates.

The Brihadaranyaka Upanishad is regarded as one of the oldest and most significant Upanishads, containing profound philosophical and spiritual teachings.

The Upanishads primarily explore the nature of reality, seeking to understand the fundamental principles that govern the universe and the relationship between the individual and the cosmos.

In the Upanishads, 'Atman' represents the individual soul, the essential self or inner essence of a living being.

The Chandogya Upanishad includes the renowned phrase 'Tat Tvam Asi,' which translates to 'That Thou Art' and signifies the unity of the individual soul with the universal consciousness.

In the Upanishads, the 'Sun' is often used as a symbol to represent the source of life, energy, and consciousness in the universe.

The Isha Upanishad includes the 'Gayatri Mantra,' which is considered one of the most sacred and powerful hymns in Hinduism, often recited during daily rituals and prayers.

In the Upanishads, the 'Moon' is often used as a symbol to represent the mind, its fluctuations, and its connection to the inner self.

The Katha Upanishad includes the story of 'Nachiketa,' a young boy who embarks on a journey to the realm of death to seek knowledge about the afterlife and the nature of reality.

In the Upanishads, the 'Stars' are often used as symbols to represent the cosmic order, the vastness of the universe, and the interconnectedness of all things.

The Mandukya Upanishad introduces the concept of 'Maya,' the illusion or veil that conceals the true nature of reality and leads to suffering.

In the Upanishads, the 'Cosmic Egg' is often used as a symbol to represent the origin of the universe, the primordial state from which all creation emerged.

The Mandukya Upanishad extensively explores the significance of the 'Aum' or 'Om' symbol, emphasizing its sacredness and its representation of the ultimate reality.

In the Upanishads, the 'Four Vedas' are revered as the sacred texts containing the knowledge of the universe, encompassing spiritual, philosophical, and ritualistic teachings.

The Brihadaranyaka Upanishad introduces the concept of 'Karma,' emphasizing the law of cause and effect and its impact on an individual's destiny and spiritual progress.