Broth
All broth is water flavored in what is essentially a brewing process to taste like something else. Practically anything will work in a broth: vegetables, herbs, spices, grains and meat (from bone). As a result, it has sometime been referred to as a watery, or thin, soup. That would also be why broth is so often used as a starter for soups (you're already half way there).
In general, broths are easy to make at home, yet most choose to buy the broth in the store since they don't have enough time to cook a broth at home. It doesn't matter where you obtain your broth since broth is a fairly safe choice for those of us eating with restrictions in our diet.
Be careful however that the broth is made with all ingredients you can eat. Quite often broth can be made with a variety of spices and herbs that you may have problems with (for example peppers) or with grains you may be allergic to (such as barley).
A little history
The word soup, meaning liquid food, is first recorded in usage in the mid-17th century. However, soup, and liquid forms of cooking, is one of the oldest forms of cooking: broth, stews, porridge, bouillon, consommé and many other liquid-type meals. Since digestion was a bit of a problem in ancient times, liquid meals came in handy since they were easier to digest.
Trivia
The word broth shares roots with the word "brew." Both come from the Indo-European base word, "bhreau-" which meant "heat" and "boil." So broth, like brew, very literally, means a liquid in which something has been boiled.
