Are you confused about the differences between a stock, a broth, a bouillon and a soup? If you are, you're not alone. There's not much agreement, even among chefs. Some say stock and broth are the same. Some say the only difference is that broth has seasoning, which stock has none. Let's start by saying that broth and bouillon are synonymous and that if broth is served as a dish in itself, then it's soup.
That leaves us with stock versus broth. If you're a home cook, there's no difference, just watch the salt, because a product labeled "broth" may be seasoned whereas one labeled "stock" may not be seasoned. Read the label.
If you are a classical French chef or aspiring to be one and using classic recipes, then there is a distinction between broth and stock that you should be aware of, and it is a distinction that is made by professional organizations such as the Culinary Institute of America and the French Culinary Institute. It's bones versus meat.
A classic or traditional stock is made from bones plus a few vegetables (usually onion, parsley, carrots, and celery) with no seasoning. The bones may be roasted for additional flavor. The aim is to get the collagen from the connective tissues, which makes a stock thick, and even gelatinous when cool. The body that this gives to a stock is its defining characteristic. A stock is not thought of as a finished product but as a base for other things such as sauces and soup.
A traditional broth, on the other hand, is the liquid in which meat has been cooked. It has basically the same vegetables as stock, but it is usually seasoned. A broth may be served as-is, in which case it is then officially a "soup". Consommé is an example.
One way of looking at it is that stocks stay in the kitchen but broths may go to the table.
Practically, in many kitchens, there may be little difference. Stocks or broths may be seasoned or unseasoned, bones with meat still attached may be used to make either. Again, for the home cook, they are usually interchangeable. "Vegetable stock" is exactly the same as "vegetable broth", since vegetables have no bones.