Pug-parser is a core component of the Pug template engine. It's responsible for taking Pug code, a concise, elegant HTML templating language, and transforming it into an Abstract Syntax Tree (AST). This AST represents the structure of the template and is then used by other Pug tools for further processing, such as code generation and optimization. Understanding the parser is essential for anyone developing tools or extensions for Pug. It's the foundation upon which Pug's powerful features are built.