Filler is the interior of a premium cigar: long leaves, not chopped scraps, in the cigars this encyclopedia is talking about. In Spanish, tripa. A blender builds filler from leaves of different stalk positions — volado for burn, seco for aroma, viso and ligero for body and strength — and from different farms and vintages.
How those leaves are arranged matters as much as which leaves they are. Entubado rolls each leaf into a tube. An accordion bunch folds them. Either way the goal is a draw you can live with and a burn that does not race down one side. Short-filler cigars exist; they are a different product.
Filler is where a house shows its hand. A puro uses filler, binder, and wrapper from one country. A blend mixes origins. Neither is a moral category. It is a recipe.