Packed tightly; jam-packed (with people or things shoved closely together), like a crowded train or a fully packed container.
通勤ラッシュで電車はぎゅうぎゅう詰めだった。
The train was jam-packed during the morning rush hour.
段ボールに服をぎゅうぎゅう詰めにして運んだ。
I crammed clothes tightly into the cardboard boxes to carry them.
ライブ会場はぎゅうぎゅう詰めで、前に進めなかった。
The concert venue was packed so tightly I couldn't move forward.
冷蔵庫の中がぎゅうぎゅう詰めで、何があるか見えない。
The refrigerator is so packed I can't see what's inside.