An effect type. Certain creatures have spirit companions, and spirit powers are used in conjunction with those companions. A creature can use a spirit power only if its spirit companion is present in the encounter. If a spirit power includes “spirit” in its range, determine line of sight and line of effect from the spirit companion’s space, which is the power’s origin square.
Published in Player's Handbook 2, page(s) 220, Rules Compendium, page(s) 120, 316.