gisshiri
Describes something filled to the brim with no space wasted. Implies thoroughness and density, often with a positive nuance.
💡Looking at a bento box — 'The bento is gisshiri packed with delicious food!'
スケジュールがぎっしり詰まっている。
My schedule is gisshiri packed.
The bookshelf was ___ filled with novels from floor to ceiling.
本棚に小説が○○詰まっている。