What is "surface mail"

n. Mail which is transported by motor vehicle, by railway, or by seacraft, but not by aircraft.

n. mail that is sent by land or sea [ant: air mail]

Surface mail, also known as sea mail, is mail that is transported by land and sea (along the surface of the earth), rather than by air, as in airmail. Surface mail is significantly less expensive but slower than airmail, and thus is preferred for large or heavy, non-urgent items and is primarily used for sending packages, not letters.