What occult science is the Arcanum 2 referring to?

Answers from the books of Samael Aun Weor

Arcanum number 2 is the Priestess, Occult Science. In the region of the Spirit, the One is the Father who is in Secret, the Two is the Divine Mother who is the Unfoldment of the Father.

Samael Aun Weor. Tarot and Cabala, chapter 2