gRPC - Remote Procedure Calls are not new, but gRPC (developed from Google around 2015) provides a very restricted interface for passing data between applications - binary compressed data for performance, has a wide adoption on many platforms. Why use it? why is it different from SOAP or REST (or GraphQL even!). Have a listen to find out more!
Here are a few links that will help take the gRPC subject further if you wish:
A great overview from Wikipedia: https://en.wikipedia.org/wiki/GRPC Bit more depth here with some examples too: https://grpc.io/docs/what-is-grpc/core-concepts/ If you don't want to read, then the MSDN Channel 9 peeps can help: https://channel9.msdn.com/Shows/On-NET/ASPNET-Core-Series-High-performance-requests-with-gRPC
Episode 7 - gRPC