Mandukya Upanisad
This Upanisad is said to contain, in just twelve verses, the gist of all the other Upanisads. It belongs to the Atharva Veda. It consists of only twelve verses and is thus the shortest of the Upanisads. Brahman (the Absolute) is identified with the term Om. The sound Om consists of three parts-A, U, and M- which are identified with Vaisvanara, Taijasa and Prajna, Unlike the other Upanisads, this one does not relate any anecdotes, imaginary dialogues, or stories to illustrate its teachings. Also unlike the other Upanisads, it is silent about rituals and worship and plunges at once into a discussion of Atman and Brahman.