Definition & Meaning of "flat brush"

What is a "flat brush"?

A flat brush is a painting tool with bristles that are wide and rectangular. It has a straight edge and is used to make bold, even strokes, fill in large areas, and create sharp lines. Flat brushes are great for painting wide areas and can also be used for details and creating textures. They are commonly used in both acrylic and oil painting, as well as in watercolor, to achieve a range of effects.