Multiprotocol Label Switching - also known as MPLS - was around before software-defined wide area networking - also known as SD-WAN - came along to provide the benefits of SDN to networking that was hardware based.
MPLS is a protocol for efficient network traffic flow that happens between two or more locations. MPLS operates in a similar way to switches and routers and is considered to be layer 2.5. Packet-forwarding technology is used to make data forwarding decisions. https://www.fieldengineer.com/sd-wan/sd-wan-vs-mpls-vs-sdn