undulation

Undulation is a wavelike motion or a wavy form in which parts of a body, surface, or field move alternately upward and downward. The word comes from Latin undula, meaning a small wave.

In physics and fluid dynamics, undulation describes the propagation of waves along a medium: strings, membranes, or fluids can support undulatory motion characterized by properties such as amplitude, wavelength, and frequency. Surface undulations in water arise from gravity and surface tension, producing crests and troughs that travel as waves. In solids, transverse or flexural undulations occur in beams, plates, and other structures, often associated with bending waves or buckling patterns.

Biology also uses the term, particularly for locomotion. Many animals propel themselves by undulation; snakes and eels generate waves that travel along the body from head to tail to produce forward motion. Some invertebrates move by undulatory peristalsis. In plants, undulation can describe wavy margins of leaves or the curving arrangement of certain stems.

Geology and geography apply the concept to terrain. The term describes gentle, wave-like variations in landscape, seabeds, or dune fields, where undulating surfaces feature alternating ridges and valleys over long distances.

In design and architecture, undulation refers to wave-like surfaces and forms that create rhythmic textures and spatial dynamics, contributing to the aesthetic and tactile character of objects and spaces.