Cardboard is a generic term for a heavy-duty paper of various strengths.
This ranges from a simple arrangement of a single thick sheet of paper to complex configurations featuring multiple corrugated and uncorrugated layers.
Despite widespread use in general English and French, the term is deprecated in business and industry.
Material producers, container manufacturers, packaging engineers, and standards organizations, try to use more specific terminology.
There is still no complete and uniform usage.
Often the term “cardboard” is avoided because it does not define any particular material. (source)
So can hamsters eat cardboard?
Yes cardboard is fine for them to chew on and eat if they like.