Multi-protocol Label Switching - Definition from the Hotspot Shield Glossary
MPLS is a protocol concerned with network traffic and ways to speed up the flow of said traffic and shape how it is formed. In traditional routing, a packet of data would have to be analyzed by a router and then forwarded on to the next stage after the router has made a “decision” on its contents and where it needs to be sent - This continual process of reviewing and decision making can cause problems and bottlenecks.
A packet that is forwarded using MLPS will be given a certain class the first time it enters a network - This class will allow a router to quickly understand how the packet needs to be handled and where it should be sent. This labeling system allows data to be transferred across a network in a more effective manor.