Cable locks are made from intertwined metal fibres which are protected against the elements with a plastic covering. They tend to be longer in length for more versatility - Small and thin or chunky and robust, there's sure to be one to suit.
They come in a variety of weights designed for specific purpose; maybe attaching to something static during a quick cafe stop or for all day protection whilst you work. Combining a cable lock with a D lock is common, as cable locks can be vulnerable to a thief with the right tools, so best to double lock. There are cable locks with a combination locking system or key locking system. Some cables require a separate padlock to complete the security.