What is Markdown?
A markup language (ML), which is used for formatting.
It can be converted to HTML, thereby formatting web pages. It almost allows focusing on the content without worrying about the format.
For programmers, this language is easy to use and efficient. Previously, it was popular among programmers and commonly used for writing documentation. Markdown documents can be said to be widespread on Github (the world's largest platform for programmers to "socialize").
Gradually, some English applications supported some Markdown formats to varying extents, including Reddit, Discord, ChatGPT, Claude...