FreeMarker is a template engine: a Java library to generate text output (anything from HTML to auto generated source code) based on templates and changing data. The .freemarker extension typically indicates a file containing a FreeMarker template. These templates use a specific syntax to embed dynamic content within static text. When the template is processed by the FreeMarker engine, the dynamic parts are replaced with actual data, resulting in the final output. FreeMarker is often used in web application development to generate dynamic web pages, emails, configuration files, and other text-based documents. It supports features like variables, loops, conditional statements, and macros, allowing for complex and flexible template designs. The templates are typically plain text files, making them easy to edit and maintain. The FreeMarker engine is responsible for parsing the template, evaluating the expressions, and generating the final output. The data used to populate the template can come from various sources, such as databases, Java objects, or XML files. FreeMarker is a powerful tool for separating presentation logic from application logic, making web applications more maintainable and scalable.