Source : Free On-Line Dictionary of Computing

transport layer
     
         (Or "host-host layer") The middle layer in the
        {OSI} seven layer model.  The transport layer determines how
        to use the {network layer} to provide a virtual error-free,
        point to point connection so that host A can send messages to
        host B and they will arrive un-corrupted and in the correct
        order.  It establishes and dissolves connections between
        hosts.  It is used by the {session layer}.
     
        An example transport layer {protocol} is {Transmission Control
        Protocol} (TCP).
     
        {OSI} documents: {ITU} Rec. X.214 (ISO 8072), ITU Rec. X.224
        (ISO 8073).
     
        (1997-12-07)