Protobuf
In plain terms
A compact, schema-driven binary serialization format from Google.
Going deeper
Protocol Buffers define data structures in a schema and serialize them into efficient binary, much smaller and faster than JSON. They power high-performance APIs.
Under the hood
Strongly typed with forward/backward compatibility via field numbers; the default payload for gRPC.
Examples
gRPC, high-throughput microservices, mobile APIs, event streaming.
Think of it like...
Like shorthand codes both sides agree on, far terser than spelling everything out.