Let's start off with a definition, since clarity is the best place to begin when cooking for a guest with certain restrictions: Veganism is a plant-based dietary strategy that excludes any and all products that come from animals. The elimination of meat is explicit, but it's worth saying that things vegetarians might eat — like eggs and dairy products — are completely off the list for vegans.
Just like any other diet or lifestyle, the definition of the diet is tailored even further on the individual level. Regardless of the semantics surrounding the word vegan, and regardless of how it's interpreted on the micro level, when it comes to cooking for your vegan (and vegetarian) family and friends, chicken broth is completely off the the table. Even a little splash. Even a little whisper.