The inner material of a veneered door, or the like. 2. A combination of utilities, sometimes including elevators, for the central stem of a building. 3. A mass of iron or other ferrous material in an electromagnet, induction coil, or transformer, serving to concentrate and intensify the magnetic field resulting from a current in a surrounding coil. 4. The molded open space in a concrete masonry unit. Also called cell. 5. An undisturbed, cylindrical sample of earth or rock obtained by means of a core drill and used for analysis and testing of bearing capacity. Also called boring. 6. The center of a plywood panel, consisting of veneers, sawn lumber, or composition board.