Line of beauty
Line of beauty is a term and a theory in art or aesthetics used to describe an S-shaped curved line (a serpentine line) appearing within an object, as the boundary line of an object, or as a virtual boundary line formed by the composition of several objects. This theory originated with William Hogarth (18th-century English painter, satirist, and writer), and is an essential part of Hogarth's theory of aesthetics as described in his 1753 book The Analysis of Beauty.