fillér, name of various small change coins through

In general, a filler is something that is used to fill gaps. Specialized meanings of the word "filler" include:

Filler (animal food), dietary fiber and other ingredients added to pet foods to provide bulk
Filler (linguistics), a sound spoken to fill up gaps in utterances
Filler (materials), particles added to a matrix material, usually to improve its properties
Fillers are mostly used in furniture industries to fill the plywood or wooden surfaces prelaminated or laminated, prepolished or polished and on all sorts of woods so that no absorbing pores or minute holes are left open. This is done prior to the application of wood polishes or finishes and wood stains so as to maintain a better look of such surfaces.
In media and entertainment:

Filler (media), in television and other media, material that exists outside the story arc to pad out other material
Filler (song) by hardcore punk band Minor Threat
Filler notes, in music, notes added between beats
Filler track, in music, an album track that is deemed not to be a major, standout song, but one to fill a void or gap
Filler, short pieces of information used to 'fill' odd gaps on the printed page of a newspaper or other publication when the main feature falls short of the full page. These can be mini-articles, jokes, cartoons, recipes, poems, usually submitted by freelance writers.
In computing:

Filler, a field used to pad out the size of a fixed width record for a file or some other storage or transmission unit. A field named Filler is commonly used in Cobol to pad out a record and adjusted in size as new fields are added within the existing length.