In simple language Paquebot means mail begins at sea, postmarked on land.
Covers and cards mailed at sea are generally referred to as "paquebot" covers. "Paquebot" is French for "packet boat," and postal administrations use paquebot handstamps to mark mail received from a seagoing vessel that has no on-board post office. First used in Great Britain in 1894, the term was adopted for general use by the Universal Postal Union in 1897.
Other paquebot markings that have been used include "Loose Ship Letters" or "Ship Mail" (Australia), "Posted at Sea" (various countries), "New York Ship" (New York City), "Schiffsbrief" (Germany and Austria), "Pacchibot" (Italy), "Paketboot" (Netherlands and colonies), "Paquete" (Portugal and colonies) and "Paquetboat" (United States).
Source : Wiki, Linns.com