Since this is a hard term for the kids to remember, we use word games to learn the definition, and we do hands on activities to demonstrate erosion.  Each student receives a sandwich bag with a piece of sandpaper and a brief instruction sheet.   We travel to the playground to spot signs of erosion; each selects a small rock to put in their baggy.  In the classroom we use the sandpaper to “weather” the rock, then we blow the debris away and shout, “erosion!”