1.NounStrong paper coated with (traditionally) sand or (today) manufactured aluminum oxide, silicon carbide, or other abrasive material, used for smoothing and polishing.
"They like to finish it off with a piece of 600-grit sandpaper before cleaning and painting."
2.NounA sheet of such paper.
"I need a scraper and a sandpaper over here."
3.VerbTo polish or grind (a surface) with or as if with sandpaper.