A markup language is a system for annotating a document in a way that is syntactically distinguishable from the text. It uses tags or codes to define elements within the document, such as headings, paragraphs, and links. Common examples of markup languages include HTML for web pages and XML for data representation. These languages help browsers and software understand how to display or process the content. Markup languages are essential for structuring information, making it easier to read and manage. They are widely used in web development, document formatting, and data interchange.