noun

• (parapsychology) A visible substance believed to emanate from the body of a spiritualistic medium during communication with the dead.
  "He saw again clearly enough[…]the doctor’s consulting room in the Avenida de la Revolución, visited for some drunken reason in the early hours of the morning, macabre with its pictures of ancient Spanish surgeons, their goat faces rising queerly from ruffs resembling ectoplasm, roaring with laughter as they performed inquisitorial operations; […]"
• (parapsychology) An immaterial or ethereal substance, especially the transparent corporeal presence of a spirit or ghost.
  "Then came some hollow groanings from inside the cabinet. The Spiritualists sat up expectantly. "That's ectoplasm," said Ogilvy. "It always causes pain on emission.""
• (cytology) The outer granule-free layer of cytoplasm.