CommonMark

For short it's the Markdown syntax standard. It replaces the old original Markdown.

CommonMark is a standard, unambiguous syntax specification for Markdown, along with a suite of comprehensive tests to validate Markdown implementations against this specification. We believe this is necessary, even essential, for the future of Markdown.

There are currently CommonMark implementations for dozens of programming languages, and the following sites and projects have adopted CommonMark: Discourse, GitHub, GitLab, Reddit, Qt, Stack Exchange, etc.