RPC stands for Remote Procedure Call. The idea is that we can invoke a function/method on a remote server. RPC is very popular for IoT devices.
What Is gRPC? — google RPC
gRPC is the latest framework to be created on the RPC protocol that is used for high-performance communication between services.
gRPC uses protocol buffers( binary messages) instead of JSON/XML.
The binary data format allows the communication to be lighter. Also, gRPC is built on top of HTTP/2, which supports bidirectional communication along with the traditional request/response.
Most modern browsers can’t provide the level of HTTP/2 control required to support a front-end gRPC client.