Definition of: golden section

1. In Euclidean geometry, the division of a line segment in extreme and mean ratio.
2. In esthetics, the division of a line or of a figure in which the smaller length or area is to the larger as the larger is to the whole; also, that proportion of a plane figure in which the smaller dimension is to the larger as the larger is to the sum of the dimensions; broadly a ratio of 3:5, thought to be especially pleasing esthetically. In sculpture, this is applied to the proportion of the frontal plane of the figure. In the Petrarchan sonnet, the relationship between the octave and the sestet is very like that of the golden section, with the 14 lines divided in a ratio of 8 : 6. (The true section of 14 is 8.65 : 5.35.) In bookbinding, the proportion of an octavo binding also approximates this ratio.