DDP is a protocol which is vastly used in a meteor. ddp protocol is highly recommended that before starting this step let’s get ourselves familiar with Meteor through this documentation.
ddp protocol was originally developed by meteor team, but there is nothing in it i.e Meteor specific. It can work with any database, framework, or programming language, and it can work on servers, clients, and mobile devices.
It is somewhat REST, but for WebSockets. It may use sock js or WebSocket protocol as a lower-level transport. Protocol explicate some guidelines for communication between client and server.