gRPC is an open source high performance RPC framework developed by Google. It uses HTTP/2 for transport, Protocol Buffers as the interface description language, and provides features such as authentication, bidirectional streaming and flow control. gRPC can connect microservices efficiently and is used by many companies including Google, Uber, Square and Netflix. It generates client and server code for multiple languages and can be used for building distributed systems like microservices architectures.