Liquid is a template engine created by Shopify and written in Ruby. It is used to build dynamic web pages and emails by separating the presentation logic from the content. Liquid templates contain a mix of HTML, CSS, JavaScript, and Liquid's own markup language. This markup language consists of objects, tags, and filters. Objects output variables, tags control the logic and flow of the template, and filters modify the output of objects. Liquid is widely used in e-commerce platforms, content management systems, and email marketing tools to generate personalized and dynamic content. Its simple syntax and secure design make it a popular choice for developers who need to create flexible and maintainable templates. The engine is designed to be secure by only allowing access to a predefined set of objects and filters, preventing malicious code from being executed. Liquid files are typically used in conjunction with backend systems that provide the data to be rendered within the templates.