YAML (YAML Ain't Markup Language) is a human-readable data serialization format commonly used for configuration files and data exchange between languages with different data structures. It emphasizes simplicity and clarity, using indentation to represent structure rather than brackets or braces. YAML supports complex data types such as lists, dictionaries, and scalars, making it a popular choice for developers who need to define settings or transfer data in a format that is both easy to read and write.