The Free On-line Dictionary of Computing (30 December 2018):

Label Switching Router

    (LSR) A device that typically resides somewhere
   in the middle of a network and is capable of forwarding
   datagrams by label switching.  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)