The term is an extension of GI which is a traditional abbreviation for Galvanized Iron.
Today the term GI typically refers to essentially pure zinc (>99%) continuously hot dip coated steel, as opposed to batch dip processes.
Zinc coated steel substrate for PPGI is typically produced on a continuous galvanizing line (CGL).
The CGL may include a painting section after the hot dip galvanising section, or more commonly the metallic coated substrate in coil form is processed on a separate continuous paint line (CPL).
However, only "pure" zinc coated steel is typically referred to as PPGI.