Kabbalah is a mystical form of Judaism. Broadly speaking, Kabbalah refers to Jewish mysticism dating back to the time of the second Temple, approximately 400 years BCE. Kaballah was a carefully guarded oral tradition before it became systematized and dispersed in the Middle Ages. The kabbalistic worldview was expressed most importantly in the Yalkut Re'uveni by Reuben Hoeshke in 1660. It also made its way into prayer books, popular customs, and ethics.
The focus of Kabbalah is the simultaneous transcendence and immanence of God, with the latter described in terms of the sefirot, or attributes of God. There are 10 sefirot, which are emanations from God through which he created the universe. Each have corresponding qualities in human beings. This hidden aspect of God and his relationship with humanity can be better understood by speculation and revelation.
The hidden side of God can be seen as the feminine side of God, which complements the masculine (or external) side revealed in the Tanach. This female side or aspect of God is sometimes called the Shekhinah ("dwelling"), which traditionally has referred to the divine presence and is associated with light.