Cardboard is a thick, stiff material made from layers of heavy paper pressed together. It's stronger than regular paper but lighter and cheaper than wood, which makes it perfect for boxes, packaging, and craft projects.

Most products you order online arrive in cardboard boxes because the material protects what's inside while being easy to fold, cut, and recycle. Pizza boxes, cereal boxes, and moving boxes are all made from cardboard. The wavy layer you can see on the edge of torn cardboard is called corrugated cardboard, and those ripples make it extra strong without adding much weight.

Cardboard is also fantastic for building and creating. Kids make forts, castles, and rocket ships from cardboard boxes. Architects sometimes build cardboard models of buildings before constructing the real thing.

When someone calls something cardboard, they might mean it seems flat or fake, like a cardboard cutout of a celebrity: it looks like the person from a distance but has no depth or realness. A cardboard character in a story is one-dimensional and unconvincing, more like a picture than a real person.