The World file is a text file in which the geo-reference of a corresponding image is given. The coordinate system used is not in this text file, but in a corresponding file or in the image itself.
The World specification was introduced by the commercial Esri. A World file can be opened in multiple applications, but compared to GeoTIFF, a World file has less support.
Optional files with a World File:
.prj: this is the usual extension for a file in which the coordinate system used (the projection) is given. If present, this is an essential file.
.aux.xml: this “auxiliary” file may contain exclusive information that cannot be stored in the World file itself, but is necessary to display the image correctly, for example, information about color usage.
.xml: in most cases, a .xml of the same name contains information that is also present in the main files. The XML is often created automatically when opening a World File in certain software. If an XML contains no additional information, this file is not relevant for preservation.
.ovr or .rrd: these are optional “pyramid” files, with which a World file can be opened faster in the application in which it was created. This file is not relevant for preservation.
TIFF World File is a non-preferred format for file type Images (georeference).