To expand upon @maartin 's list, here is a list of many of the common implementations to have extended Markdown to include Definition Lists, with a link to their docs
| System | Support | link to documentation |
|---|---|---|
| Pandoc | YES | Pandoc - Pandoc User’s Guide |
| Wordpress | YES | Markdown Quick Reference Cheat Sheet – Support — WordPress.com |
| Python-Markdown | YES | Definition Lists — Python-Markdown 3.3.4 documentation |
| php Markdown Extra | YES | PHP Markdown Extra |
| MultiMarkdown | YES | Definition Lists |
| SGML Markdown | YES | Markdown Definition List Examples |
| Maruku | YES | |
| kramdown | YES | |
| Markdown-it | YES | GitHub - markdown-it/markdown-it-deflist: Definition list (<dl>) tag plugin for markdown-it markdown parser |
| Gitlab | On roadmap | GitLab Content Editor | Strategy (&5401) · Epics · GitLab.org · GitLab |
| CommonMark | No | Description List - Extensions - CommonMark Discussion |
| Github | No |
Even though W3C decided to change their name to Term-Description Groups in HTML5, Definition Lists are a commonly used extension. The discussion on CommonMark above has been looking at implementing this since 2014, and they are only holding back in case some implementations find the ‘back-tracking’ hard to implement. GitLab are looking at it already, and once CommonMark adopts it the people like Github who follow CommonMark will do the same, so it’s only a matter of time.
It would be great to add Obsidian to the list of software that supports it - is the feature already available in any of the parsing libraries Obsidian uses?