Backus-Naur Form

Backus-Naur Form as defined by Wikipedia:

In computer science, Backus-Naur Form (BNF) is a metasyntax used to express context-free grammars: that is, a formal way to describe formal languages.

BNF is widely used as a notation for the grammars of computer programming languages, instruction sets and communication protocols, as well as a notation for representing parts of natural language grammars.