A pastry brush is a kitchen tool which is intended for use with pastry. Many pastries need to be glazed or brushed with things like egg whites, melted butter, or milk. A pastry brush controls the amount of glaze which is applied, and ensures that it is spread evenly and efficiently. Keeping a pastry brush or two around is very useful, even if you do not do that much baking, because there are a number of potential uses for a good pastry brush.
Many baked goods are finished with a glaze which creates a distinctive crust. Pies, for example, can be brushed with egg whites or milk for a glossy finish. A pastry brush is also used in the assembly of dishes which require phyllo dough, and it can be used to add delicate glazes to things like cakes. As a general rule, it is a good idea to keep multiple sizes around, ranging from a small, thin brush to a wide brush with a large area of coverage.
This kitchen tool is essentially the same thing as a basting brush, a brush designed for applying bastes, marinades, and glazes to meats and savory foods. Cooks often keep separate sets of pastry and basting brushes to minimize the potential for flavor contamination. However, if you have a set of brushes made from silicone, you will not need to keep them separate, since silicone does not hold flavors or odors. Otherwise, you may want to consider color coding your basting and pastry brushes, to ensure that you do not introduce barbecue sauce to your scones.