...an exit visa.是什么意思？

...an exit visa.

出境签证

an

art. 一（在元音字母前代替不定代词a），一任一某一，一个；

例句
He started eating an apple...
他开始吃苹果。

exit

n. 出口，通道，退场，退去，退出，死亡；vi. 离开，退出，退场，去世；

例句
They escaped through an emergency exit and called the police.
他们从紧急出口逃脱，并报了警。

visa

n. 签证；vt. 签发签证；

例句
He had lived illegally in the United States for five years after his visitor's visa expired.
在访问签证到期后，他又在美国非法居住了5年。