ephemeral port

from The Free On-line Dictionary of Computing (8 July 2008)

ephemeral port

   <networking> A {TCP} or {UDP} {port} number that is
   automatically allocated from a predefined range by the {TCP/IP
   stack} software, typically to provide the port for the client
   end of a {client-server} communication.

   {BSD} used ports 1024 through 4999 as ephemeral ports, though
   it is often desirable to increase this allocation.

   (http://ncftpd.com/ncftpd/doc/misc/ephemeral_ports.html).

   (2002-10-06)