'Postal Union' definitions:

Definition of 'Postal Union'

From: GCIDE

Postal \Post"al\, a. [Cf. F. postal.] Belonging to the post office or mail service; as, postal arrangements; postal authorities. [1913 Webster]
Postal card, or Post card, a card used for transmission of messages through the mails, at a lower rate of postage than a sealed letter; also called postcard. Such cards are sold by the government with postage already paid, or by private vendors without a postage stamp. The message is written on one side of the card, and the address on the other.
Postal money order. See Money order, under Money.
Postal note, an order payable to bearer, for a sum of money (in the United States less than five dollars under existing law), issued from one post office and payable at another specified office.
Postal Union, a union for postal purposes entered into by the most important powers, or governments, which have agreed to transport mail matter through their several territories at a stipulated rate. [1913 Webster]