Quote Originally Posted by gr82bart
What is "POP"? I searched google, but I only came up with softdrinks.
Printing out Paper. Usually this refers today to Centennial POP, which is a gelatin silver chloride paper manufactured by Kentmere and sold by Chicago Albumen Works, but albumen and Ziatype are also printing out processes. POP develops during the exposure without requiring a developer, and then it is toned and fixed.

Normal paper is DOP--developing out paper.