gRPC is a high-performance RPC framework built on HTTP/2 that uses Protocol Buffers for serialization, enabling efficient communication between services across multiple languages. Unlike REST APIs that rely on JSON over HTTP/1.1, gRPC leverages binary encoding and multiplexed streams for lower latency and higher throughput. Protocol Buffers (protobuf) serve as gRPC's interface definition language (IDL), providing strongly-typed contracts that generate language-specific code automatically. The framework supports four distinct communication patterns—unary, server-streaming, client-streaming, and bidirectional streaming—making it ideal for microservices, real-time systems, and high-load distributed architectures. A key insight: gRPC's performance advantage stems not just from HTTP/2, but from the tight integration between protobuf's compact binary format, efficient code generation, and built-in features like connection multiplexing, flow control, and deadline propagation.