We, as consumers (and crafters) call this cardboard:

It's a cardboard box right?
Well, yes and no.

We as consumers refer to this as cardboard. But, people in the industry refer to this as a corrugated box. It is made of corrugated cardboard. It is a sandwich of two sheets of kraft paper, with a fluted sheet of kraft paper in the middle.

This next picture shows what the industry calls cardboard.

We commonly call this "Cereal Box Cardboard." Which is quite ok. But the technical name for it is simply cardboard!

Think of it in as a similar thing to card stock, just thicker.

Here on this website the cardboard crafter uses both of these types of materials for projects. Each has it's own distinct advantages and characteristics. SO.... be sure to save up both your corrugated boxes and your cardboard boxes!! Like I do!