Chesed, Mercy or loving-kindness, is the fourth sefirah and the first below the abyss, the highest of the seven sefirot that pertain to the created world. It heads the right-hand Pillar of Mercy beneath Chokmah and expresses expansive, benevolent, unbounded love, the outpouring generosity of the divine, grace given without measure. In the Kabbalistic scheme of balances Chesed's limitless giving must be checked by the severity of Geburah opposite it, for mercy without judgement would dissolve all form; the health of the Tree lies in the equilibrium of the two.
Chesed is also called Gedulah, greatness. Its divine name is El, the simplest name of God, associated with mercy and might. The sefirah takes its place in the doctrine set out in the Sefer Yetzirah and developed by the medieval Kabbalists; in the moral and psychological readings the Kabbalah gives the Tree, Chesed is the principle of benevolence, abundance and the open hand, the grace that founds the created order before it is given shape by the discipline of the sphere below.
Sources The ZoharTraditionally attributed to Moses de Leon with Sefer Yetzirah: The Book of Creation in Theory and PracticeAryeh Kaplan