Markdown

2022-03-28

Markdown is a lightweight markup language for creating formatted text using a plain-text editor. John Gruber and Aaron Swartz created Markdown in 2004 as a markup language that is appealing to human readers in its source code form. [9] Markdown is widely used in blogging, instant messaging, online forums, collaborative software, documentation pages, and readme files.
Wikipedia

Obsidian uses Markdown as the file format for notes. It uses some proprietary formats to link notes together, but, for the most part, it's entirely text-based.