Hollow Core Construction : Panel construction, particularly common in doors, in which an open lattice of wood or sometimes paperboard rings is faced with plywood, hardboard, or some similar material
Ralph W. Burklin & Robert G. Purington, Fire Terms: A Guide to Their Meaning and Use, National Protection Association, Boston, MA 1980 USA. (Guide: Meaning and Use, Nat Prot Association Fr Srvc - Amer) {457}