These ex-officers often gather to reminisce about their military days.

ex-officers 是由前缀 ex-（表示"前、前任"）和名词 officers（军官）组成的复合名词。ex- 表示"从前的、不再担任的"，officers 指"军官"。 ex-officers 指"前任军官"，即"退伍军官"。