Source : Free On-Line Dictionary of Computing

Label Switching Router
     
         (LSR) A device that typically resides somewhere
        in the middle of a {network} and is capable of forwarding
        {datagrams} based upon a label.  In many cases, especially
        early versions of {MPLS} networks, a LSR will typically be a
        modified {ATM} {switch} that forwards datagrams based upon a
        label in the {VPI}/{VCI} field.
     
        (1999-06-14)