A shoot-'em-up is an informal name for a simple action game — on a computer, a phone, or an old coin machine — where you fire at wave after wave of enemies. The job is to shoot as many as you can, not to solve a puzzle or tell a long story. People also use it for loud action films that are mostly gunfights. It is casual, and a little old now; younger players more often say shooter. The 'em is a spoken form of them: shoot them up. It is one nickname, not a sentence you say in class about real guns.

射擊遊戲（一直開槍打敵人的那種）