I apologize if I'm asking a question that's been discussed before. I searched and didn't find my answer though.

What exactly is MDO playwood? My wife and I picked up a plan for a mail box where the planter should be constructed with MDO plywood. We went to Lowe's to pick up materials and no person at that store could tell us just what MDO plywood is. How do we know what to buy? Thanks in advance for your help.