Refers broadly to artworks in a variety of styles that incorporate some aspect of motion, including machines, mobiles, and actual objects in motion. Orginating between 1913 and 1920 with the works of Marcel Duchamp, Naum Gabo, and Vladamir Tatlin, the style reached its peak in the 1960s.

Source: AAT

http://vocab.getty.edu/page/aat/300069473