A Context-Free Grammar (CFG) is a formal system used to define the structure of languages, particularly in computer science and linguistics. It consists of a set of rules or productions that describe how symbols can be combined to form valid strings. Each rule specifies how a single non-terminal symbol can be replaced with a combination of terminal and non-terminal symbols. CFGs are essential for parsing and interpreting programming languages, as they help in understanding the syntax of code. They are also used in natural language processing to analyze and generate human languages. By providing a clear structure, CFGs enable the development of compilers and interpreters for various programming languages.