The word Upanishad is derived from upa (nearby), and nishad (to sit-down), that is, "sitting down near". Groups of pupil sit near the Guru to learn from him in the Guru-shishya parampara or tradition.
The Upanishads mark the culmination of Indian thought and are the final parts of the Vedas. As the Upanishads contain abstract and difficult discussions of ultimate philosophical problems, they were taught to the pupils at the end.
There are more than 200 known Upanishads, one of which, the Muktika, gives a list of 108 Upanishads. This number corresponds to the holy number of beads on a mala or Hindu rosary.
The Upanishads form an important part of literary legacy. They deal with questions like the origin of the universe, life and death, the material and spiritual world, nature of knowledge and many other questions.
The earliest Upanishads are the Brihadaranyaka which belongs to the Sukla Yajur Veda and Chand yogya which belongs to the Sama Veda. Some of the other important Upanishads are the Aitareya, Kena, Katha Upanishad.