Quick breads use leavening agents other than yeast to provide texture to the finished product. They are called "quick" because they do not require the traditional rising and kneading procedures of yeast breads. Leavening is achieved through the action of one or more additives that create airiness and light texture to baked goods. Baking soda paired with an acidic ingredient of some type, baking powder, eggs, or even steam can serve this purpose. Many quick breads incorporate fruit or vegetable ingredients like bananas or zucchini to give the bread a moist quality.
Breads of this type fall into three main categories which are primarily a function of how they are made. Muffin-type recipes are made by mixing all liquid ingredients together and all dry ingredients together and then combining the two mixtures. Cake-type recipes are made by whipping together fats, eggs, and sugars until the mixture is somewhat light and fluffy, a process known as creaming. The other ingredients are then added to this mixture. Biscuit-type recipes are made by mixing chilled fats with dry ingredients and then adding liquids.
Of course, these are very broad categories. While most quick breads share certain common ingredients, including fats, leavening agents, flour, eggs, and a liquid, there are thousands of different recipes and variations of these types of baked goods. Muffins and cakes invariably incorporate sugars, and many recipes call for other ingredients that influence flavor or texture in some way.
Almost any type of baked item with a bread- or cake-like texture is classified as a quick bread. Muffins, cakes, banana and zucchini bread, and even brownies are quick breads. Technically, pancakes, biscuits, and waffles are also. Some quick breads are more like traditional yeast breads, such as Irish soda bread, corn bread, or beer bread. Many cookies and other sweet baked goods might be called quick breads as well.
Sometimes, unleavened breads like flatbreads, communion wafers, or tortillas are mistaken for quick breads. They are not, however, as they do not contain any kind of leavening agent. The only true requirement for classification as a quick bread is the lack of added yeast and the absence of kneading. This means that other specialized baked goods, like popovers and cream puffs, are also quick breads.