ectoplasm, in occultism, a mysterious, usually light-coloured, viscous substance that is said to exude from the body of a spiritualist medium in trance and may then take the shape of a face, a hand, or a complete body. It is normally visible only in the darkened atmosphere of a séance (q.v.). Ectoplasm is said to be the substance involved in the materialization of spiritual bodies, and the levitation of material objects is commonly explained by the gradual buildup of columns of ectoplasm underneath the objects. At the end of a séance the ectoplasm disappears, allegedly by returning to the medium’s body.