In woodworking and cabinetry, an overlay refers to how much a cabinet door covers or overlaps the cabinet frame when it is closed.
A 1″ overlay means that the cabinet door is 1 inch wider and 1 inch taller than the cabinet opening, so it overlaps the frame of the cabinet by 1 inch on all four sides when it is closed. This is also sometimes referred to as a full overlay.
Overlay is an important consideration when choosing cabinet doors because it affects the overall look and functionality of the cabinets. Different overlay sizes can create different styles and provide varying levels of accessibility to the contents inside the cabinet.