Thanks for posting here!
Microsoft Q&A users need the ability to stay updated on the content relevant to them. One of the ways is using the following functionality that supports a user to follow a Q&A question, tag, or user.
It simply means that you have interacted with the thread and it will pop up in the "questions I follow" menu on your home page.
I hope I could help you out.
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)