Markdown is a lightweight markup language created by John Gruber and Aaron Swartz in 2004. The primary goal of the MD format is to allow users to write content using an easy-to-read, plain text format that can be easily converted into structurally valid HTML or XHTML. Files with the .md extension are essentially plain text files that utilize specific, simple syntax (such as asterisks for bold/italic, hash symbols for headings, and hyphens for lists) to denote formatting. Because of its simplicity and reliance on plain text, MD files are highly portable, future-proof, and extremely popular for documentation, especially in the software development world (e.g., README files on GitHub). They are also widely used for note-taking, blogging, and creating static site content. Any standard text editor can open and edit an MD file, though specialized Markdown editors offer real-time previewing capabilities.