Far as I know, "kitty grass" is a generic term; it may be wheat, it may be barley. I always got the barley back when I got kitty grass.

I use Barley Cat instead, now. Shake it over their food.

This is NOT where I buy it, just a link to show you what I am talking about:
http://www.google.com/products/catal...ed=0CHUQ8wIwAQ

To answer your specific question, wheat grass is the young wheat plant.