ESRI (makers of ArcGIS) defines georeferencing as "Aligning geographic data to a known coordinate system so it can be viewed, queried, and analyzed with other geographic data." Plainly, this means that georeferencing allows to you import historical maps or aerial photos into a GIS project!
The MSU workshop will guide you through the process of georeferencing an historic map using QGIS in order to view changes to our north campus through time.
Update: If you are using a newer version of QGIS than what is depicted in this video, install the plugin "QuickMapServices" instead of OpenLayers (which doesn't exist any more).