Haml (HTML Abstraction Markup Language) is a templating engine designed to simplify and streamline the creation of HTML documents. It is primarily used in web development, particularly within Ruby on Rails and other Ruby-based frameworks, although implementations exist for other languages as well. Haml aims to reduce the amount of repetitive and verbose code typically associated with HTML by using a concise and elegant syntax based on indentation. Instead of closing tags explicitly, Haml relies on indentation to define the structure of the HTML document. This leads to cleaner, more readable code that is easier to maintain. Haml also supports features like variables, loops, and conditional statements, allowing developers to create dynamic and reusable templates. It encourages DRY (Don't Repeat Yourself) principles by allowing the definition of reusable components and partials. Haml files are typically preprocessed on the server-side to generate standard HTML, which is then sent to the client's browser. The 'haml' extension signifies that the file contains Haml code that needs to be processed by a Haml engine before it can be rendered as HTML.