A caster is an undriven, single, double, or compound wheel

Wheel

A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

 that is designed to be mounted to the bottom of a larger object (the "vehicle") so as to enable that object to be easily moved. They are available in various sizes, and are commonly made of rubber, plastic, nylon, aluminum, or stainless steel.

Casters are found in numerous applications, including shopping cart

Shopping cart

A shopping cart is a cart supplied by a shop, especially supermarkets, for use by customers inside the shop for transport of merchandise to the check-out counter during shopping...

s, office chair

Office chair

An office chair, or desk chair, is a type of chair that is designed for use at a desk in an office. It should be comfortable and adjustable and can swivel 360 degrees.-History:...

s, and material handling

Material handling

-Material Handling Industry:Material Handling is the movement, storage, control and protection of materials, goods and products throughout the process of manufacturing, distribution, consumption and disposal. The focus is on the methods, mechanical equipment, systems and related controls used to...

 equipment.