Packet trade generally refers to any regularly scheduled cargo, passenger and mail trade conducted by ship. The ships are called "packet boats" as their original function was to carry mail.A "packet ship" was originally a vessel employed to carry post office mail packets to and from British embassies, colonies and outposts. In sea transport, a packet service is a regular, scheduled service, carrying freight and passengers. The ships used for this service are called packet ships or packet boats.