Twig is a template language for PHP that aims to be fast, flexible, and secure. It addresses some limitations of using PHP as a templating language by providing a more concise, template-oriented syntax with features like inheritance, macros, and filters. Templates are compiled to optimized PHP code for faster performance. Twig also includes security features like sandboxing to restrict what template code can do. The language provides common programming constructs like conditionals, loops, and expressions to build dynamic templates.