strategy of holing up in a castle or building
Refers to a defensive tactic of barricading oneself inside a fortification or building, often in a siege context. Can be used figuratively for staying put and refusing to come out.
The enemy forces adopted a strategy of holing up in the castle.
He decided to barricade himself in his house.
籠城 is the act of holing up or being besieged; 籠城作戦 is the deliberate strategy or plan to do so.
Compound of 籠城 (ろうじょう, 'holding a castle') and 作戦 (さくせん, 'strategy').