What is a concealed hinge and hidden frame system?

Concealed hinges are fully mortised into the leaf and frame so nothing is visible when the door is closed, and they are usually three-way adjustable for perfect reveals. They require a stronger leaf — typically 40 mm or more with a dense core — and precise machining. Combined with a flush concealed frame they produce the seamless, handle-less look specified in most high-end villa and apartment projects.