cardboard
n. uncountable A2 Elementary US //ˈkɑɹdˌbɔɹd// UK //kˈɑːdbɔːd// card·board
n. a thick, stiff paper used to make boxes. It is stronger than normal paper but still easy to cut and fold.
n. a heavy-duty paper-based material of various thicknesses, typically used in the manufacture of packaging and shipping containers.
I need a large cardboard box for these books.
The delivery arrived in a sturdy cardboard carton reinforced with heavy-duty plastic tape.
The artist chose to work with recycled cardboard rather than traditional canvas, finding that the rough texture added a raw, industrial quality to the final installation.
From card + board.
Usage
Uncountable when referring to the material itself; countable only when referring to specific types or items in technical contexts.