surface mail
noun [ U ] uk/ˈsɜː.fɪs ˌmeɪl/ us/ˈsɝː.fɪs ˌmeɪl/
平邮，平信，普通邮件
a way of sending letters, parcels, etc. by road, sea, or train and not by aircraft, or things sent in this way
I sent the parcel by surface mail. 我用平邮把包裹寄了出去。
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