I'm glad you posted about this--i was wondering what other people called it too. In motobu udundi, my sensei has always just called it "ayumi" or walking, along with the other walking techniques. Our really basic one is one diagonal step to enter, one continuing step to unbalance, and then a step at 90 degrees to take down or throw. This is the same walking pattern that shows up in okinawan dance, which has led to a lot of speculation...