The étagère became a popular form of furniture in the 19th century.  The word derives from the French meaning to arrange on different levels or stages.  Consisting of open shelves and sides, and often without a back panel, étagères were used to display collections and knickknacks so prevalent in Victorian times.  This one is on casters. A caster is an assembly that includes a wheel along with a mounting system, such as a bracket or fork, and sometimes additional features like a swivel mechanism or brake.  Casters are designed to provide both mobility and flexibility when attached to furniture.