PACKET, or PACKET-Boat, a vessel appointed by the government to carry the mail of letters, packets, and expresses, from one kingdom to another by sea, in the most expeditious manner. Thus, the packet-boats, under the direction of the post-master-general of Great Britain, carry the mails from Dover to Calais, from Falmouth to Lisbon, from Harwich to Helvoetsluys, and from Parkgate to Dublin.