Stouts are an extra dark, multi-beer that are made basically by roasting the malts. That's how you get the dark, roasty character, traditional in stouts. There are many different kinds of stouts. Some of which include wheat stout or the milk stout. That actually has lactose in it. That's where the name milk stout comes from. That's going to be sweet, creamy. A really nice mouth feel.
Then you have your dry Irish stout, and for that you can think Guinness. It's going to be better but it's really creamy, often times, you'll want that on a nitrogen pour, which just gives it really fine bubbles. Which allows it again, to have a real creaminess into the mouth feel.
Then you get into what is commonly referred to as just stout with no qualifier or it can be called an American stout and export stout. There again, especially with the American version, it's going to be roasty. You're going to get a lot of roast character. It's also going to be highly hop. You will get a lot of, you know, a lot of bitterness to kind of balance against that roast.
Again, that's going to be, traditionally, what you get if you walk into a bar and ask for a stout. It's going to be hoppy and it's going to be bitter and all of those flavors are going to balance against each other.
There's also the Russian imperial stout. That's a stout that pretty much originated by the English brewers who were exporting their stronger porter, in fact, they called it a "stout porter". Stouts were originally referred to as stout porters, meaning "stronger", "more".
You know, a stout porter, but in the beers that they were exporting to Russia, they wanted the extra strong stouts. Now we have a style of beer called the Russian imperial stout, which is very high in ABV. Again, you can get a lot of variants in terms of hops in there but it's not going to be as high as say the American hops but it's so going to be quite a presence and you're going to get a higher alcohol content in a lot of that roasting as that comes through.
That's a refine down of what a stout is.