I should probably add something about that to the post.

Sorta like the Tor version of DNS. It's where your Tor goes to get information about an onion, e.g. how to connect to it. Tor versions that don't support v2 will refuse to host this information, and so if all 6 HSDirs of an v2 onion doesn't support it, the onion will be unreachable.

Maybe understanding a bit about how onion services work will help: https://community.torproject.org/onion-services/overview/

According to Google, it's either a high school directory or a hidden service directory.

Since we’re discussing TOR it’s probably the latter