The Upanishads are ancient Sanskrit texts that form the philosophical foundation of Hinduism, exploring concepts like Brahman (ultimate reality), Atman (self/soul), karma, and moksha (liberation). While they influence religious thought, their primary subject is metaphysical philosophy - the nature of existence, consciousness, and reality. Law, politics, and other worldly subjects are addressed in other texts like the Dharmashastras or Arthashastra, not the Upanishads.