Backus-Naur Form (BNF) is a notation used to express the grammar of programming languages and data structures. It provides a formal way to describe the syntax rules, using symbols to represent different elements. Each rule consists of a left-hand side, which is defined by a name, and a right-hand side, which shows how that name can be constructed using other names or symbols. BNF is particularly useful in the fields of computer science and compiler design, as it helps in the creation of parsers that can interpret code. By using a clear and concise format, BNF allows developers to understand and implement the structure of languages effectively.