airmail; air service; flight (for mail/goods)
Refers to mail or cargo sent by air, or the air transport service itself. Often used in contexts like 飛行便で送る (send by airmail).
Please send this parcel by airmail.
If sent by airmail, it will arrive tomorrow.
船便 means surface mail (by ship), contrasting with 飛行便 (airmail).
Compound of 飛行 (hikō, 'aviation, flight') and 便 (bin, 'mail, service'). The reading ひこうびん follows standard on'yomi.