Casi's right in that it could be both but I believe that 'solid' in carpentry/furniture building is usually meant to denote that the piece of furniture is made from pieces of solid oak lumber/pine lumber/beech lumber/chestnut lumber/etc as opposed to oak plywood or veneers//pine plywood or veneers//beech plywood or veneers//etc
Thank you Riverkid and I wish a very happy New Year!