wikipedia provides a good explanation, quoted below:
. In the U.S. solid wood frame and panel
construction, using either mortise and tenon
or cope and stick
jointed frames, is traditional, with maple, cherry, oak, birch, and hickory among the most commonly used species. Mortise-and-tenon frames, with their greater strength and permanence, are more costly to produce and less commonly used as compared to cope-and-stick frames. As an alternative, miter joint
frames, which may be identifiable by face-surface relief that follows continuously around the frame, have become popular. Miter-jointed frames typically employ embedded metal fasteners to secure frames elements (stiles and rails) cut at a 45 angle. Captured within frames, panels may be either solid or veneered engineered wood (either particle board or medium density fiberboard). Laminates, including those designed to resemble hardwood, can typically be identified by a more rounded appearance associated with the minimum bending radii necessarily entailed by the manufacturing process of applying laminate to an underlying substrate. By comparison, solid surfaces, and solid hardwoods in particular, can be milled with more sharply defined corners, edges, or grooves on either a panel or frame.
- Panels. Panels used in frame-and-panel kitchen cabinet doors may be fashioned either of solid wood or covered by paint, veneer, or laminate in which case they are fashioned of engineered wood. The panels are typically not fastened with glue or nails but rather "float" within the frame to accommodate seasonal expansion or contraction of the wood frame.
- Solid-door construction. Doors may be fabricated of solid material, either engineered wood (particle board or medium-density fiberboard, but not typically plywood) or solid wood. Engineered wood panels may either be used as slabs or may be shaped to resemble frame-and-panel construction. In either case, engineered wood panels are generally painted, veneered, or laminated. Solid wood panels are typically formed of multiple boards of the selected wood species, jointed together using glue and may either be painted or finished. Solid wood construction offers the possibility of refinishing in case of damage or wear.
- Decorative panels. Cabinet doors panels can be used decoratively on cabinet sides, where exposed, for a more finished appearance.
- Glass door construction options. Doors may have glass windows constructed of muntins and mullions holding glass panels (as in exterior windows). Other designs either mimic the divided-light look of muntins and mullions with overlays, or may dispense with them altogether. Cabinets using glass doors sometimes use glass shelves and interior lighting from the top of a cabinet. A glass shelf allows light to reach throughout a cabinet. For a special display effect, the interior rear of a cabinet may be covered with a mirrors to further distribute light.