A soup spoon is rounder and a little larger; better for soup I think because it holds a little more of all the goodies in the soup. Here's a picture of the difference in size:

A five piece place setting will include a soup spoon, dinner spoon, salad/dessert fork, dinner fork and knife.

The soup spoon shown on top of the dinner (or teaspoon) spoon is actually a cream soup spoon. There is another soup spoon that is shaped like the dinner spoon but larger that can be used for other-than-cream soups, chilli, chowder, etc. I've been collecting cream soup spoons because I love their shape.

I believe that a standard five piece place setting is made up of a dinner fork, knife, dinner spoon, teaspoon and dessert fork. Soup spoons are an extra piece. Most people use the dinner spoon for soup.

In English style services, the round spoon is a soup spoon, the other is called a dessert spoon. No distinction is made between cream soups and other kinds.

A five piece place setting can be anything you choose! It depends on what you decide when you register your pattern. I chose luncheon knife and fork, salad/dessert fork, teaspoon and butter knife. I am currently helping a friend who chose a seafood fork as her 5th piece and wants soup spoons by cruising ebay for her.
That piece which Sharon/chase calls a dinner spoon is often called a place spoon and more recently an oval soup spoon. I grew up calling it a dessert spoon...my mother would say "do you want to eat your soup with a dessert spoon or a soup spoon?" LOL!
Here are some pieces in a pattern I am collecting for my grandndaughter.

The silver superstore (which is a wealth of info) lists a five piece place setting for stainless as
"5-pc Place Set includes:
Salad Fork, Dinner Fork, Dinner Knife, Oval Soup Spoon, Teaspoon".

I really like the round spoon, however, much more than the oval soup spoon.
And iced teaspoons. I love those!