The origin of port style wine and fortification is as follows...
England got into a little spat with France and France stopped shipping over their wines. So the English, still wanting their 'claret' wines, got in touch with some other neighboring countries and asked them to send over their wines. Portugal answered the call, but the fastest method of transporting wines was by sailing ships. Since the journey took a while and the heat was a little more intense around Portugal compared to France, some innovation was needed for the wine to travel safely and not spoil. The Portuguese fortified their wine with neutral grape brandy, increasing the alcohol content, protecting the wine from spoilage, and creating what has now become a specialty style wine known around the world (named 'Port' for the Portuguese that developed it).
Wine fortification, as Waldo noted, means adding some kind of neutral alcohol into standard wine to boost the alcohol levels. Neutral grape brandy is what is commonly used for port wines from a traditional and commercial standpoint. Port wine tends to be described as both sweet and higher in alcohol content today (generally above 16%).
In my humble opinion, I'm going to guess that the fair is using the category of 'fortified' for dessert wines in general, but a phone call to them would likely be the best.
- Jim