Questions & Answers about Cartonul este în cutie.
Because Romanian usually puts the definite article at the end of the noun, not before it.
- carton = a carton / cardboard
- cartonul = the carton / the cardboard
The ending -ul is a common definite article ending for masculine/neuter singular nouns.
A useful thing to know: carton is a neuter noun, and neuter nouns in Romanian behave like masculine in the singular and feminine in the plural. That is why you get cartonul in the singular.