A course grinding material used to figure, shape, or finish optical elements. According to Wikipedia, an abrasive is a material, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away. Here finishing a material means polishing it to gain a smooth, reflective surface. The process can also involve roughening as in satin, matte or beaded finishes.
In optical communication industry abrasive materials can be silicon carbide, aluminum oxide, silica, cerium oxide, emery or rouge. Abrasives differ from polishing materials mainly in particle size and are often referred to as a measured “grit”.