covering letter
noun [ C ] UK uk/ˈkʌv.ər.ɪŋ ˌlet.ər/ us/ˈkʌv.ɚ.ɪŋ ˌlet̬.ɚ/ (also covering note); (US cover letter, cover note)
附函，附信
a letter that contains information about the thing it is sent with
Please send a covering letter with your application form. 请将附函与申请表一同寄出。