Ectoplasm is the very thin, watery outer layer of a cell. Biologists use the word ectoplasm primarily to talk about amoebas.
Ectoplasm and endoplasm, or "dense inner section," are found in the tiny cells known as amoebas. An amoeba's movements are a result of the way these inner and outer layers fit together. A much less scientific meaning of ectoplasm is "visible spiritual energy." 19th- and early 20th-century spiritualists claimed that a gauzy ectoplasm formed during trance states, a visual connection between living and spirit worlds. This ectoplasm was often proven to be made of cheesecloth.