Not just bread... any food that contains wheat, barley, rye (and a few other lesser-known grains) or ingredients made from them. Here's a list for starters:
bagels, muffins, croissants, hamburger buns, scones, pizza, pasta, noodles, cakes, pies, cookies, crackers, hot dogs, deli meats, any breaded foods including but not limited to chicken nuggets and fish sticks, and beer. Then there are the "hidden" gluten sources like malt flavoring within otherwise "safe" corn or oat breakfast cereals or hydrolyzed vegetable protein in soy sauce.
While you can pretty readily find gluten-free versions of many processed foods in the grocery store now, you'll find they're mostly low in fiber vital to blood sugar, weight, and cholesterol control and in nutrients that are essential to good health. They're often higher in sugar and calories, too, so weight gain is a real threat. The best gluten free foods are "whole" fresh foods, unadorned.
It's not an easy diet, and it's one that has only been proven useful for those with celiac disease or genuine wheat sensitivity.
"We can complain because rose bushes have thorns, or rejoice because thorn bushes have roses." Abraham Lincoln