Definition of "acellular"

Acellular background is that which is still present when the cells are removed from the microscope.

1999 — Shore SL, Bolsover S (1999). "Understanding Maps of Physiological Cell Signals". In Mason WT. Fluorescent and Luminescent Probes for Biological Activity. Biological Techniques Series (2nd ed.). London: Academic Press. p. 100. ISBN 9780080531779. — via Google Books (Preview)

The superficial portion of this epithelium is acellular and consists of thin, keratinized fibrous plates which have become artifactually detached during slide preparation (Plate 59, p. 361).

1985 — Meyer, David B. (1985). Laboratory Guide for Human Histology. Detroit, Michigan: Wayne State University Press. p. 28. ISBN 9780814318010 – via Google Books (Preview).