If we hide header, no way to know on which site/app we are. I am not sure if its from same company or not.
There are definitions on net, from my understanding its design canvas where each element has its own Information and Interaction. It sounds very similar to Vector definition (A quantity having direction as well as magnitude).
one of the best beautiful part of it, that this stands out from crowd. Even Metro concept has came from Railway station and Airport where we can find signboards whch stands out from these heavily public places and guide us to achieve our goal.