It's a tamper that helps me push down my greens heavy smoothies.  My mother accidentally broke my old one by sitting it in the blender and then accidentally turning it on, leaving it with a huge hole in it and pretty useless.

It's the same one I had, just new.  I've had a Vitamix for 10 years now and use it every day, sometimes 2-3 times a day.  It's an essential piece to the Vitamix.  I cannot make my smoothies without it.