The name for this peculiar gravitationally repulsive state is not well-established. Sandra Faber referred to it as a vacuum with a finite energy density, and sometimes as a false vacuum. In my own technical articles I call it a false vacuum, although I have to explain that for most inflationary models this usage stretches the meaning for which the phrase had previously been used in particle physics. In this article I will refer to it as a repulsive-gravity material. It may seem strange to see the words "vacuum" and "material" used to describe the same thing, but keep in mind that this stuff is strange. The word "vacuum" is used to emphasize that it is different from ordinary matter, while I am calling it a material to emphasize that it is different from an ordinary vacuum!