Hi aaron-k, to answer your question about fortified wine it is wine to which alcohol has been added, perhaps in the form of a distilled alcoholic concoction, such as a brandy (that has a relatively high alcohol content).
When one normally makes wine they add yeast to the grape juice and let it ferment (it will do so from the natural yeast, but one usually prefers a yeast that gives a better flavor).
Eventually it stops fermenting (making alcohol) when the alcohol level gets high enough to kill the yeasts (usually about ten percent alcohol or so). Yeast are lousy environmentalists and they pollute their environment until they die. That is NOT a political statement.
But the level of alcohol in 'regular' wine is not enough to stop bacterial growth, and 'regular' wines will go bad shortly (within hours to days) of opening.
Why anyone would ever let wine hang about that long is beyond us here, but some people apparently do.
Wines in casks are also subject to the same bacterial infestations.
To preserve wines, folks found that adding some more alcohol to the wine could make the product relatively immune to bacteria.
And so we have fortified wines that are generally labelled as sherry, port, Marsala, vermouth, or Madiera.
The alcohol level in those wines is often about 18 percent or so, enough to give the bacteria a fatal hernia, or something like that.
Those wines generally last for quite a long time after opening.
Both regular and fortified wines can be used for cooking, and both add different nuances to the food.
As far as cooking wine goes, they used to carry it in the supermarkets I worked in many years ago that could not legally sell wine.
And the other posters, as usual, are correct, it is wine with a whole bunch of salt, and was legal because no one on anything but a down and out bender would ever drink the stuff. Even then, most of those guys would drink after shave or mouthwash or other products that usually contained alcohols that caused far more damage than ethanol, and much more quickly. That is how lousy the cooking wine tasted, I suppose.
Anyway I hope this answers your question.