Bina, usually translated as "understanding", is the cognitive faculty that develops and articulates the seminal energy of chochma so that the latter becomes known, in a detailed conceptual way, through bina. Bina is also the inductive and deductive faculty of understanding (or deducing) one thing from another, thus expanding the point of chochma into a multi-dimensional conceptual system. The Zohar therefore symbolizes chochma and bina and their relationship as "the supernal point (chochma) within its palace (bina)" (Zohar 1, 6A). However, bina is not merely an adjunct to chochma, it involves as well the ability to intuit a more inclusive reality that than encoded within chochma itself.

Bina is also the ability to explain the concept to another person, thus "reproducing" it. In this sense bina is referred to as "the mother of children" (Psalms 113:9).
~ Taken from Ten powers of the soul

  Bina on the tree of life is ‘understanding’. She is Yin energy, compassion, pure love, The Cosmic Mother. She is the attentiveness to comprehend, understand and intuit. The key symbol of Binah is the Yoni, or female generative organ, indicating that this Sephira is the energy from which all life emerges. Bina reflects the ultimate bi sexuality of the soul.
  As the Golden Dawn Knowledge lecture states: "in Binah is a thick darkness which yet veileth the Divine Glory in which all colours are hidden, wherein is mystery and depth and silence, and yet it is the habitation of the Supernal Light." In this sense, Binah is described as the Outer Robe of Concealment, an idea which might most readily be understood by considering the extent to which our physical forms conceal our inner realities from others.  she is the Sanctifying Intelligence.
  In the sense that Binah is the giver of life, she is the Bright Fertile Mother. But in the sense that she restricts and disciplines (in effect, is the first lawgiver), she is called the Dark Sterile Mother.
  In short bina is the understanding of the wisdom of Chokmah. She is the mother darkness of space that births life, the mystery of silence and depth. She intuits and understands as is the manner of the feminine. The Yoni is her symbol the sacred depth of deep pleasure and cauldron of life. As the mother who understands her own nature hence understands her children.