An MPLS, or Multi Protocol Label Switching, nework protocol. It is in essence, an alternative to local router configuration needed to use a group of VPN's for accessing assets between sites. Using this method, MPLS clouds allow a full mesh of sites. A single large outgoing connection to the internet which makes it more reliable and cheaper than a VPN network across multiple sites.
The Technical Breakdown
Normally, large multi site networks are made with site-to-site leased lines or VPNs. Which is something that requires alot of routers and configurations. With MPLS the entire network is meshed together. Making the entire thing a single "network", even with different types of data circuits. This is performed by the WAN marking data packets with virtual labels. These are used to move the data between network nodes. This makes things both more efficient and more secure on a private network which is actually seperated from the general internet. Within MPLS the forwarding is based on the label, rather than a full IP address which cuts down on transfer speed.