Answer:
All breads have at least two ingredients: some kind of flour--example, wheat, spelt, etc.--and some sort of moistener--example: milk, water, etc. Beyond this, you can do almost anything with bread. You can add leaven (yeast, baking soda/baking powder), you can add things for texture: eggs, milk, butter, etc.. You can also add nuts, fruits and candy.
So there are sweet breads, whole grain breads, flat breads, unleavened breads, breakfast breads, English muffin bread, biscuits, scones--you get the picture.
-Hope that helped. :)