Is gelatin vegetarian?

Gelatin is collagen extracted from animal skin, bone and connective tissue, then broken down until it dissolves in hot water and sets as it cools. That setting behaviour is the entire reason it exists in food.

It is not meat, it does not taste of anything, and it disappears into the texture of whatever it is in. Which is precisely why people who have avoided meat for years discover it in something they have been eating happily.

Where it turns up

Gummy sweets and marshmallows, obviously, once you know.

Less obviously: some yoghurts, where it is used as a thickener. Mousses and fillings. Jelly, of course. And the capsule shells of a great many supplements and medicines, which is the one people almost never check.

The pattern is that gelatin is structural rather than the point of the product. A fruit sweet reads as a plant product. A low-fat yoghurt reads as dairy, and dairy is fine for vegetarians, so nobody looks further.

Which animal, and why the label will not say

Almost always pig or cow. Fish gelatin exists and is used where pork must be avoided, but it is the exception.

“Gelatin” on its own satisfies the ingredient declaration rules, so the label usually will not tell you the source. If you need to know for religious observance, the ingredient list is not enough and the manufacturer or a certification mark is the answer.

What replaces it

Pectin from fruit, agar and carrageenan from seaweed, and various starches. Products using these usually advertise it on the front, because for the audience that cares it is a selling point.

That gives you a useful signal in reverse: a gummy sweet that says nothing about being vegetarian on the front probably contains gelatin.

More on the ingredient itself is on the Gelatin page, and the general problem, that “vegan” is not a legally defined word while “gluten-free” is, is on the page for people avoiding animal ingredients.