Cardboard refers to a thick and stiff type of paper usually used to make boxes, packaging, or other similar materials. It is often brown in color and provides strength and protection for items. Full definition
I had the chance to create a «kitten castle» out of cardboard boxes for one of my kitten pods. (catdepot.org)
A few years ago, to his benefit, he started painting on bronze casts of cardboard boxes as well as canvas. (nytimes.com)
The cards were stored in custom CD jewel cases with booklet inserts and then packaged in cardboard boxes about half the size of the old CD long boxes. (gamesetwatch.com)