What is Markdown?

Plain text with just enough punctuation to imply formatting, which is why it ended up as the default for READMEs, issues, wikis and notes. Its tables are the awkward part - a pipe-and-dash grid that's readable enough written by hand and tedious to maintain by hand.

What is CSV?

The least glamorous and most durable data format there is: rows of values separated by commas, readable by every spreadsheet and database ever written. All its subtlety is in quoting - a value with a comma in it has to be wrapped in quotes, and a quote inside that has to be doubled.