What does "postal" mean?

Postal: Belonging to the post office or mail service; as, postal arrangements; postal authorities. Postal card, or Post card, a card sold by the government for transmission through the mails, at a lower rate of postage than a sealed letter. The message is written on one side of the card, and the direction 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.