I need Information about "Combo Door Box car".

Is there anybody who can explain me the meaning of “Combo Door Box car”. Im from Germany and need the information for describing the Athearn N scale model.

One plug door and one sliding door. The plug is only opened when needed to get the load in, otherwise it is just like a regular boxcar.

http://www.usatrains.com/r19300combodoor.html

Thank you for information!