just a note...we were always taught in school that the p in pH stood for potential as in the potential of Hydrogen. having to do with the addition of or removal of Hydrogen ions to/from a solution making it either acid or alkaline.
I looked it up with the intention of using it as a question and the article I read basically said that they weren't sure. It named 3 or 4 potential answers (of which "potential" was 1), but said that there wasn't a definitive favorite.