Upanishads as Brahman

In Vedanta, the word Satyam (Reality) is very clearly defined and it has a specific significance. It means, that which exists in all the three periods of time (the past, present, and future) without undergoing any change; and also in all the three states of consciousness (waking state, dream state and deep-sleep state). This is, therefore, the absolute Reality ,birthless, deathless and changeless referred to in the Upanishads as Brahman