Grit size is often a term used in sandpaper. It is usually defined as a certain amount of grits per square inch. The more grits per square inch the "finer" the sandpaper is. Low grit counts are often just used for really abrasive or rough surfaces. Some sites post grit size charts as well for all of your measuring needs. Check out http://www.cs.rochester.edu/u/roche/rec.wood.misc/grit.sizes.html
. for a grit chart.
