Is gelatin vegetarian? I understand that vegetarians are against meat, and gelatin is derived from meat and bones. So the obvious answer is "no."

But I'm not entirely sure. What constitutes an ingredient as "vegetarian" or "vegan?"
Without further qualification, if someone refers to themselves as vegetarian (in America), the general assumption is that they are lacto-ovo vegetarian. That means they don't eat animal products that require killing the animal, but eggs and dairy are fine. Gelatin comes from a dead animal (unless they start harvesting it with arthroscopic probes :), so it is not a vegetarian ingredient. There are many other hydrocolloids, such as agar, that can be used to produce similar textures if needed.