Sat means that which is: being, the real, the true. The Chāndogya Upaniṣad teaches that in the beginning there was only being, one without a second, from which all things came. In Vedānta, sat is the first element of saccidānanda, and the real is defined as that which does not change or cease.
Sat
Being, reality or truth: in Vedānta, the pure existence that is the ground of all that exists.