Definition - What does Supreme Self mean?
Supreme Self is a term which can be used interchangeably with the terms, Brahman or Paramatman, the latter of which comes from the Sanskrit roots parama, meaning “supreme,” and atman, meaning “self." All of these terms refer to a concept of an infinite Consciousness or Soul, which is inseparable from the rest of the universe and is without personality, ego or individuality.
This concept is often referenced in yoga because the purpose of a spiritual yoga practice is to find unity with the Supreme Self and to recognize one’s true nature.
Yogapedia explains Supreme Self
There are many connotations and qualities surrounding the concept of the Supreme Self. It is generally agreed upon that the Supreme Self is infinite. It has boundless substance, life and consciousness, and exists in an endless space. It may be described as the “Atman of all atmans," or the Self of all selves.
It is said that the "negative" (or more precisely, apophatic) aspects the Supreme Self are that it is infinite, formless, without characteristics and invisible. Its "positive" (or cataphatic) attributes are truth, bliss, peace and knowledge. The Supreme Self can also be compared to ether, in that it is considered to be omnipresent, all-pervading and eternal.
A disciplined yoga practice and consistent practice of meditation can help one connect more deeply with the Supreme Self. Advanced yogis exist in this state of Self-realization before moving on to enlightenment and moksha (liberation from the cycle of life and death).