Da'at is a "conjectured" sephirah that falls on the path of Gimel. In Hebrew, Da'at is "knowledge, perception, or learning." It is not really a sephirah; it is a "result" of it's location on the Tree of Life. It is midway on the longest path, and central in the upper hexagonal array. Binah and Chochma straddle the polarity between undefined knowledge and differentiation; Keter and Da'at straddle the polarity between cosmic consciousness and individual consciousness.
Da'at really is knowledge in the "Biblical Sense-" it is the focal point of the mystical union that is prescribed for sanctified couples to perform on Shabbat night, consummated at the darkest hour.
This joining opens a path for the Shekhina - a Hebrew word for the immanent aspect of the Creator, seen in Jewish philosophy as the female aspect of God. The "above" aspect of Shekhina is Binah, and the "below" aspect is Malchut. (ifdawn.com)