The history of this beer is as clear as a glass of good black stuff. There are very few details of which we can be certain. There is a traditional belief, strongly held by many, that stout is the offspring of porter. But there are some pretty good reasons to question it. How it came to be called stout is less clear but it is known that many porters brewed with higher gravities were called "stout porters." If the porter as progenitor theory is false, it is apparent that stout was originally used as an adjective to describe the great black beer.
Exactly when and how it was shortened to stout is impossible to say.
Have you ever wondered why draught stout seems creamier and the head thicker than bottled stout? Even the most casual beer drinker can notice the difference. A well-pulled draught stout should be creamy with a thick, persistent head while stout from a bottle will seem more bubbly and less silky with a shorter-lived head. This is because draught beer is infused with beer gas, a blend of nitrogen and carbon dioxide while bottled beer is carbonated with carbon dioxide alone.
The primary difference between stout and porter has traditionally been gravity. Until recently stout was only brewed with very high gravities but many brewers, especially American micros, are brewing very nice stouts with relatively normal gravities. Consistent across all stouts is black unmalted barley. This contributes most of the color and flavor characteristics common in all stouts.
A great number of adjuncts from coffee to oatmeal to milk sugar have been added with fine results.
The head of stout should be thick and is usually tan to brown. Its body should be very dark brown or black. Stouts are typically opaque but if any light does find its way through the beer should be clear.
The nose should be grainy and can carry hints of coffee, chocolate, licorice, and molasses with no apparent hops. The flavor is similar to the nose and should be rich and full. The mouthfeel should be anything but watery. A good stout can be silky, full, and creamy.
Stout's complexity makes it an excellent companion for a wide variety of foods. Stout can be paired with chocolate, meat prepared almost any way, and oysters. I've heard that a stout float is a marvelous thing but I've never been able to bring myself to dump a scoop of ice cream in an otherwise perfect pint.