Markdown is a lightweight plain-text formatting language created by John Gruber in 2004. It lets you write formatted documents using simple, readable punctuation: wrap text in **double asterisks** for bold, prefix a line with # for a heading, wrap code in backticks. The plain text is then converted into clean HTML by a Markdown parser. The genius of Markdown is that it's readable even without rendering. A Markdown source file makes intuitive sense to a human reader — unlike raw HTML, which is cluttered with tags. This makes it ideal for writing documentation, README files, blog posts, notes, and any content that needs to be both human-readable in source and cleanly formatted when rendered. Markdown is now the universal writing format for developers and technical writers: GitHub renders .md files automatically, static site generators like Jekyll, Hugo, and Next.js use it as the content format, documentation platforms like GitBook and Notion support it natively, and messaging tools like Slack, Discord, and Reddit use subsets of Markdown syntax.