filler Definition

1. A person or thing that fills.
2. A paste-like substance used for filling cracks or holes, usually in walls of buildings.
3. A material or substance used to add bulk or weight to something, or to fill a gap or space, etc.

Example: Duck down was used as a filler for the duvet
Thesaurus: stuffing, padding, packing, caulking.
4. An article, photograph, clip, etc used to fill a gap between main features in a newspaper, or a TV or radio programme.