A Reinforced Wood is a the upgraded version of Old Wood and can also be upgraded further into Metal Reinforced Wood. It can not be crafted using other materials, the only ways to obtain Reinforced Wood are through upgrading Old Wood or using the Creative Menu.
Reinforced Wood can be created by simply clicking on Old Wood with wood plank in hand.
It is possible to upgrade Reinforced Wood into Metal Reinforced Wood. For upgrade you will need 1 Scrap Iron.