For the Teaching forum there are several tags I would suggest.
“Video Course”, and “Written Course”, or maybe just “Video” and “Written”, as that would help people who strongly prefer one type of learning over another.
“Basic”, “Intermediate”, and “Advanced” for marking the level of the teaching being offered.
Depending on how many tags you’re looking to add, putting in tags for the type of topic might be helpful. Things such as “2D Art”, “3D Art”, “Animation”, “C#”, “Lighting”, “Shaders”. Though this may be something too specific that would be better covered in the titles of the threads.
When looking at the General Discussion and/or Game Design forums, these are some of the ways I tend to classify web pages and other resources I have saved for future review. These are the kinds of boxes I would tend to put Unity threads into as I was creating them or reading them.
“Advertising”, “AI”, “Business”, “F2P”, “International”, “Kickstarter”, “Legal”, “Level Design”, “Marketing”, “MMO”, “Mobile”, “Monetization”, “Multiplayer”, “Polish”, “Testing”.
As an example, there was a recent thread discussing the Red Cross and how they had asked that their symbol be removed from video games. To me, that would be under “Legal” and perhaps “Business”.