Apple's product naming is confusing.

Does anyone know what "Air" means?

I thought it used to mean smallest and lightest. But on the Mac the "MacBook" is smaller and lighter, and on the iPad we have the smaller iPad Mini, and the "iPad" is smaller and only 14 grams heavier.

From the MacBook Air line, we understood the definition to be "it's the cheap one", but that doesn't apply to the iPad line where it costs more.

So what does "Air" mean? It's there to "pad out" the product line? :/