Protocol Buffers (protobuf) is a language-neutral, platform-neutral, extensible mechanism for serializing structured data. It's similar to XML, but smaller, faster, and simpler. You define how you want your data to be structured once, then you can use special generated source code to easily write and read your structured data to and from a variety of data streams and using a variety of languages. Protocol buffers are often used for defining data structures in network protocols, configuration files, and data storage. They provide a way to efficiently serialize and deserialize data, making them suitable for high-performance applications. The main advantage of protobuf is its efficiency in terms of both size and speed compared to other serialization formats like XML or JSON. The schema definition is done in a .proto file, which is then compiled using the protoc compiler to generate code in various programming languages like C++, Java, Python, Go, and more. This generated code provides methods for serializing and deserializing data according to the defined schema.