Stocks and broths come in many varieties including chicken, beef, mushroom, vegetable and more. The flavor is typically achieved by simmering ingredients in a large pot then straining the solid pieces out.
Vegans can enjoy stocks and broths made with vegetables and herbs only. There are many stock concentrates (cubes, pastes and powders) on the marketplace as well that are suitable for vegans. Personal favorite is Better Than Bouillion veg paste (not the chicken one!).
Restaurants regularly use chicken stock or broth for MANY things. It’s worth asking if the broth used is vegetable based if you are ordering a soup.
Adding a rind of parmesan cheese is another way to add flavor to a stock, especially popular in Italian cuisine. That would not be vegan, but a waiter or waitress may not realize.
The lesson is, always ask.