packing; filling material
Technical term for material used to fill a space, cavity, or container, such as in packaging, construction, or dental contexts.
The packing in this box is recycled paper.
In dental treatment, a filling material is placed into the cavity.
詰め物 is a more general, everyday term for stuffing or padding, whereas 充填物 is a technical term often used in industrial or medical contexts.
Compound of 充填 (filling, packing) + 物 (thing, material). The exact historical derivation is uncertain, but the word follows standard Sino-Japanese word formation patterns.