A material's brittle if it's liable to fracture when subjected to stress. That's, it's little tendency to deform (or strain) before fracture. This fracture absorbs relatively little energy, even in materials of high strength, and usually makes a snapping sound. When used in materials science, it's generally applied to materials that fail in tension rather than shear, or when there's little or no evidence of plastic deformation before failure. When a material has reached the limit of its strength… (More on Brittleness)