Spiritualism

"A belief that departed spirits hold intercourse with mortals by means of physical phenomena, as by rapping, or during abnormal mental states, as in trances, or the like, commonly manifested through a medium; spiritism."

- Webster.

Spiritism: "The theory that mediumistic phenomena are caused by spirits of the dead." 

- Webster.

NOTE - "The very central truth of Spiritualism is the power and possibility of spirit return, under certain conditions, to communicate with those in the material form." 

- N. F. Ravlin, Spiritualistic lecturer, of California.