A chain is a series of connected links which are typically made of metal. A chain may consist of two or more links.
Chains are usually made in one of two styles, according to their intended use:
Those designed for lifting, such as when used with a hoist; for pulling; or for securing, such as with a bicycle lock, have links that are torus shaped, which make the chain flexible in two dimensions (The fixed third dimension being a chain's length.)
Those designed for transferring power in machines have links designed to mesh with the teeth of the sprockets of the machine, and are flexible in only one dimension. They are known as Roller chains, though there are also non-roller chains such as block chain.
Two distinct chains can be connected using a quick link which resembles a carabiner with a screw close rather than a latch.