The philosophy propounded in the Upanishads is known as

The Upanishads are commonly referred to as Vedanta. 

The Upanishads alone are widely known and among the most important literature in the history of Indian religions and culture and their central ideas are at the spiritual core of Hindus.

The upanishads are a part of the Vedas and are ancient Sanskrit texts that contain some of the central philosophical concepts and ideas of Hinduism, some of which are shared with Buddhism, and Jainism.