Straight from Wikipedia: "Motorcycle frame sliders are an optional tool used on street motorcycles for the purpose of maintaining the bike's side fairings and internal components in the event of a crash or preventing damage from dumping (dropping) the bike. The frame sliders are usually located and installed on the engine bolts on the left and right side fairings. The average frame sliders will run about $30 - $50 USD. "
Use the search function on here and you will find looks of examples. Just an extra layer of protection to take the brunt of the impact in a crash/tip over and save your plastics, engine cases, etc.....