Wet Plate Processing is a photographic technique, utilizing physics and chemistry to preserve imagines. It was invented in mid 19th century England. (Reference to The Era of Wet-Plate Collodion Processing)
The goal is to preserve the image on a glass plate or coated metal sheet. In this process, the photographer first coats the plate with Collodion, then moves on to sensitize, expose, develop, fix, and finally rinse it. During these ten minutes or so, the glass plate remains wet. Hence the name “Wet Plate Processing” which is short for its full name “Wet Plate Collodion Processing”.