Markup languages are systems for annotating a document in a way that is syntactically distinguishable from the text. They are primarily used to format text and structure content, making it easier for machines to read and interpret. Common examples include HTML and XML, which allow users to create structured documents that can be displayed on the web or processed by various applications. These languages use tags to define elements within a document, enabling the separation of content from presentation. This separation allows for greater flexibility and reusability of content across different platforms and devices, enhancing the overall user experience.