Moddir is a function of Europa Universalis II that allows the user to specify a directory to EU2 for it to look for its many data files in. Moddir was added as a feature in EU2 1.05, so you cannot use it on a lower version. It allows you to specify a certain directory to start EU2 in. This is almost only used by mods . All of the popular EU2 mods now use moddir.