Sight size (measurement)

Refers to the dimensions of an object that are visible to the eye, as distinct from the actual size of the object. It is typically used to describe the dimensions of the portion of a two-dimensional work of art that are visible within the window of a frame or mat, not including those parts of the work that are hidden by the rabbet of the frame or the area of the mat. It may also be used to describe the frame or mat itself, referring to the size of the opening through which a work of art would be seen.