A decoiler is a device that helps to unwind and pay out metal coils or other material such as paper or plastic film. It is used to hold the material while it is being fed into a machine such as a roll former, which will then shape it into a desired product. The decoiler helps to maintain a constantly tight coil during this process, which prevents the material from becoming damaged or deformed. It also allows for a more efficient and accurate feeding of the material into the machine.