It’s where you post a new note without tagging someone as a sort of covert reply to their note

We learned about it from Nostrasia™️ as it comes from japanese online culture where you want to reply or engage with someone or their idea without tagging them directly as a form of courtesy (i guess not “blowing up their notifications”)

Us westerners don’t tend to use them out of courtesy though, it’s often more for passive aggressive argumentation 😞