Protocol Buffers are a data interchange format created by Google that focus on efficiency, both in data size and serialisation cost. Think "super-efficient JSON or XML". Apple created a Swift plugin for the protobuf compiler, and in this screencast you can see how easy it is to start using protobufs in your Swift-based apps.
This is a companion discussion topic for the original entry at https://www.raywenderlich.com/5011-using-protocol-buffers-in-swift