Answer: frequently vegan.
Like our previous question of pasta, this one is pretty broad. In this question and answer, we’ll just focus on the traditional loaf of bread. Not quick bread (which isn’t a bread at all), buns, muffins or sweetbread (ewww, nasty). Bread is traditionally made with flour, water, yeast, sugar and some type of fat. Other ingredients often used in home baked bread are milk, eggs and butter. You will need to ask about most home baked breads. One of my favorite home baked breads is frequently vegan, sourdough potato bread. Some good stuff!
Store bought breads, pre-sliced in plastic bags, are a different story. These breads usually do not contain milk, butter and eggs. But they frequently contain honey and some potentially non-vegan dough conditioners or additives. Again, read those labels closely.
Result: potentially vegan friendly, read those labels.