Adi Shakti is the primordial energy that came out of the absolute nothingness and the entire universe formed out of this energy. If you subscribe to the “Big bang Thoery” of the formation of the universe, Adi Shakti is the energy that caused the Big Bang.
In the beginning there was nothingness. This nothingness is not empty nothing, it is a dimension beyond space and time out of which emerged the dimension of space and time which is our universe. This nothingness is the Absolute or Sunyata and out of which emerges the energy of creation. In Sanskrit it is the “Purusha and Prakriti” or the source of consciousness and the universal one consciousness.
Conceptual definition of this undefinable truth usually leads to disputes and arguments. It is better to access this information with the Aware mind and make sense out of it with the intuitive mind by completely keeping the logical, analytical mind quiet in a meditative state. As one goes deeper and deeper with the meditative practice, one can experience, at least momentarily, the state of samadhi in which this truth can be experienced and realised.
The meaning of Adi Shakti is a subject matter that needs experiencing and realising rather than studying and understanding.