Is this soup, stew, or something else?

It's a hot pot or steamboat as we call it in Malaysia. It's a clear soup made from stock. Raw ingredients are gradually added to it as it simmers. Soup and the cooked ingredients are fished out when they are done (each time when the pot boils). At the end, you are left with a rich, delicious soup that has flavours of all the ingredients intermingled and it is usually eaten with noodles.

Going by this, it would be classified as a soup or broth. It wouldn't be a stew as flour has not been used to thicken it.

It's definitely a kind of soup or stew.

The image you picked specifically calls it a "hot pot".

http://www.thetabletopcook.com/images/tabletop-cooking-homemade-taiwanese-hot-pot.jpg

Hot Pots are classified as "stews" according to Wikipedia:

Hot pot (also known as steamboat in Singapore, Malaysia, Thailand, the Philippines and Brunei), refers to several East Asian varieties of stew, consisting of a simmering metal pot of stock at the center of the dining table. While the hot pot is kept simmering, ingredients are placed into the pot and are cooked at the table. Typical hot pot dishes include thinly sliced meat, leaf vegetables, mushrooms, wontons, egg dumplings, and seafood. Vegetables, fish and meat should be fresh. The cooked food is usually eaten with a dipping sauce. In many areas, hot pot meals are often eaten in the winter during supper time.

But I'd argue that they're more soup-like. They remind me a lot of a Mexican dish called "caldo de pollo/res", which is literally "chicken/beef broth".

From the definition of "stew":

Stews are similar to soups, and in some cases there may not be a clear distinction between the two. Generally, stews have less liquid than soups, are much thicker and require longer cooking over low heat. While soups are almost always served in a bowl, stews may be thick enough to be served on a plate with the gravy as a sauce over the solid ingredients.

Your image, and this one of caldo are very broth-y, which is why I think they're more like soup.

That is certainly a stew. I might further refer to that as a hot-pot if the ingredients were raw before added to the broth, particularly if it's cooked at the table.

That particular dish looks to me like Chinese hot pot, or a similar Asian hot pot (not to be confused with Lancashire hotpot, which is a kind of stew!).

The main feature of the dish is that you have a pot at your table with a burner underneath, and a number of raw ingredients which you add to the broth and pull out at your own convenience. These may include meat, root vegetables, leaf vegetables, noodles, eggs, seafood or fish.

I would argue that it's not a soup or a stew, because the components are fished out and eaten, and are the main part of the dish. You can optionally drink the broth when you are finished, and I guess you could call that part of the dish a soup (though I would say "broth" to connote the thin-ness), but the dish as a whole is just hot pot. You don't call it a stew when you boil ravioli, right? ;)

From Wikipedia:

Hot pot (also known as steamboat in Singapore, Malaysia, Thailand, the Philippines and Brunei), refers to several East Asian varieties of stew, consisting of a simmering metal pot of stock at the center of the dining table. While the hot pot is kept simmering, ingredients are placed into the pot and are cooked at the table. Typical hot pot dishes include thinly sliced meat, leaf vegetables, mushrooms, wontons, egg dumplings, and seafood. Vegetables, fish and meat should be fresh. The cooked food is usually eaten with a dipping sauce. In many areas, hot pot meals are often eaten in the winter during supper time.

As far as I concerned it's Tom Yum Soup

http://www.bbc.co.uk/food/recipes/tomyumsoup_85069

http://en.wikipedia.org/wiki/Tom_yum