Markdown

Markdown is an plain-text syntax for writing structured texts that are both human-readable as plain-text and machine-readable for automatic parsing into different formats (HTML, PDF, ...).

For a standardized syntax definition, check out the CommonMark project. They have a quick Markdown syntax overview that also links to a 10 minute tutorial.

Markdown is used extensively in many projects, e.g. for writing this mdbook or for writing README.md files with GitHub flavoured Markdown on GitHub. As it literally takes no more than 10 minutes to learn the basics and a couple of minutes to look up anything that is a bit more complicated (for example tables in GitHub flavoured Markdown), it is really worthwhile checking it out.