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.
偵探穿著便衣工作。
Security personnel often blend in plain clothes at events.
安保人員在活動中常穿便衣混入人群。