Wood veneer is made from peeling strips of wood off a tree like you pull paper towels off a roll. As a result, it's much thinner than solid wood and is typically applied to plywood or particleboard to give it strength. It has two main advantages over solid wood: it can cost less and its grain can be more consistent. It also is less affected by humidity and temperature than solid wood.
You can stain wood veneer to match a solid wood door and use it on the side panels. Make sure both the veneer and the door are made from the same wood species.
Wood veneer also makes an attractive option for cabinet interiors visible through glass doors.