A bureau or department of government, or under governmental superintendence, whose office is to receive, transmit, and deliver letters, papers, and other mall-matter sent by post Also the office established by government in any city or town for the local operations of the postal system, for the receipt and distribution of mail from other places, the forwarding of mail there deposited, the sale of postage stamps, etc. post office department. The name of one of the departments of the executive branch of the government of the United States, which has charge of the transmission of the mails and the general postal business of the country. post office order. A letter of credit furnished by the government, at a small charge, to facilitate the transmission of money.