Label Switch Routers - Definition from the Hotspot Shield Glossary
LS Routers can quickly route data packets on a network due to the pre-determined label that has been designated to that packet. In traditional networking and routing, packets of data have to be identified by a router, and the router has to determine which path the data takes. In LS networks, that identification and checking does not have to take place due to the appendage of labels.
There are several different types of LS Routers that are located at different points in a network - An Ingress LSR is situated at the entry point of an LSP, a transit router is found in the center of an LSP and sends packets onto their next destination, a penultimate router is the second-to last stop in and LSP, and an egress router is the exit point; this router sends the traffic on using standard IP routing.