Dwarf refers to a person with one of several varieties of a specific genetic condition called dwarfism. A dwarf has disproportion of body parts. This is generally caused by a genetic or nutritional disability. Any adult human below the height of 4'10 (147 cm) is considered a dwarf.
One Piece has a great story and does not have a lot of filler episodes.
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.