MPLS (Multiprotocol Label Switching) – It is a way of data caryng in demandings networks. It works between 2. and 3. ISO layer. It encapsulate package in to MPLS LSP.

Normaly, every router when receive package perform lookup to find best path and forward to next hop. MPLS works on different way. Only first router search for best path, then add all hops to packet (or encapsulate packet in MPLS Label Switched Path), last router remove it, and all other routers just forward package according to data from package, without performing lookups.

Read More:
MPLS for Dummies
MPLS FAQ For Beginners