"fg-optional-mp-zombie-03.bin" refers to a specific commonly found in FitGirl Repacks of various video games—most notably the Call of Duty series (like Black Ops II or III ).
or an explanation of how to use this file during a game installation? fg-optional-mp-zombie-03.bin
In this context, the file represents optional "Multiplayer" (MP) and "Zombie" data that users can choose to skip during installation to save space. Since this file could relate to a few different things, "fg-optional-mp-zombie-03