PLAN (from Lat. planus, flat), a diagram on a flat surface; hence by analogy any deliberate scheme or design. In architecture, a " plan " is a horizontal geometrical section of the walls of a building, or indications, on a horizontal plane, of the relative positions of the walls and partitions, with the various openings, such as windows and doors, recesses and projections, chimneys and chimney-breasts, columns, pilasters, etc. This term is sometimes incorrectly used in the sense of design (q.v.).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)