plain clothes

US /ˌpleɪn ˈkloʊðz/
UK /ˌpleɪn ˈkloʊðz/
"plain clothes" picture
1.

便衣, 常服

ordinary clothes, not a uniform or special costume

:
The detective was working in plain clothes.
侦探穿着便衣工作。
Security personnel often blend in plain clothes at events.
安保人员在活动中常穿便衣混入人群。