IPA: /ˈfɪlɪŋ/
KK: /ˈfɪlɪŋ/
A substance or mixture used to fill something, such as food in pastries or a material in a cavity.
The pie was delicious, especially because of the sweet apple filling inside.
Filling → It is formed from "fill" (from Old English "fyllan", meaning to make full) and "-ing" (a suffix used to form nouns indicating an action or process). The word "filling" refers to the process of making something full or the material used to fill something.
Think of the action of 'making full' ('fill') and the process indicated by '-ing' — that's why filling means the act of making something full.