Storage space that does not contain significant data but is needed to comply with length requirements or is reserved to fulfill some future need.

1. An inert material added to paper, resin, bituminous material, and other substances to modify their properties and improve quality.

2. A material used to fill holes in wood, plaster, or other surfaces before applying a coating such as paint or varnish.

The rod used to deposit metal in a joint in brazing, soldering, or welding. Also known as filler metal.