1. A photomechanically produced plate for pictures or type made by exposing a gelatin film under a negative, hardening it with chrome alum, and printing directly from it.
2. also he·li·o·typ·y (-tī'pē) The process of producing a heliotype.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.