Markdown files are plain text files with a bit of formatting in them.
For example:
**bold** → bold
*italic* → italic
# Heading → a heading
- item → a bullet point
[link](https://example.com) → a clickable link
They can be read by both humans and machines.
Markdown files are commonly used for documents, README files, tools like Obsidian and Logseq and websites. Wikipedia, for example, consists entirely of markdown pages. A markdown file can start with so-called YAML frontmatter, but it doesn’t have to.