Diakka. Called by Occultists and Theosophists “spooks” and “shells”, i.e., phantoms from Kâma Loka. A word invented by the great American Seer, Andrew Jackson Davis, to denote what he considers untrustworthy “Spirits”. In his own words: “A Diakka (from the Summerland) is one who takes insane delight in playing parts, in juggling tricks, in personating opposite characters; to whom prayer and profane utterances are of equi-value; surcharged with a passion for lyrical narrations; . . . morally deficient, he is without the active feelings of justice, philanthropy, or tender affection. He knows nothing of what men call the sentiment of gratitude; the ends of hate and love are the same to him; his motto is often fearful and terrible to others—SELF is the whole of private living, and exalted annihilation the end of all private life. Only yesterday, one said to a lady medium, signing himself Swedenborg, this: ‘Whatsoever is, has been, will be, or may be, that I AM.; and private life is but the aggregative phantasms of thinking throb- lets, rushing in their rising onward to the central heart of eternal death’ (The Diakka and their Victims; “an explanation of the False and Repulsive in Spiritualism.”) These “Diakka” are then simply the communicating and materializing so-called “Spirits” of Mediums and Spiritualists.

Source: H.P.Blavatsky - The Theosophical Glossary